A magus has a talisman, he dies.
What happens to that talisman?
Can it be used as a magic item by another magus is it was enchanted as such?
Can another magus atune it as a talisman for their use?
Will await reply 
Tyrrell invokes serf's parma and then answers:
What happens to that talisman?
Probably nothing, there are flaws that take your items with you but if the character doesn't have one of these flaws their talisman is likely to survive their passing.
Can it be used as a magic item by another magus if it was enchanted as such?
Certainly, that finding magus may need to investigate the item to learn its powers but there is no reason why anyone should not be able to use the powers of the item, (unless they were enchanted to have use restricted to certain characters only).
Can another magus atune it as a talisman for their use?
No, a magus must always open their own talisman for enchantment someone else's talisman was clearly opened by someone else. I also do not believe that it is even possible to instill effects into someone else's talisman (but you might want to double check me on this).
I agree with Erik, with the additional note that any Personal-range effects that were designed to affect the magus rather than the talisman itself will not be usable by anybody else. This could very significantly reduce the usefulness of the device to other magi, even though they are still left with an unusually powerful device.
Just imagine for a minute finding Verditius's talisman, or Mercere's (though they're both likely to have been carefully preserved by their respective houses).
Can you fool a Talisman into thinking you are it's creator
by using a Muto Vim spell?
I assume that the person doing so foregoes the use of their own Talisman (if they have one) , while the spell is in effect.
My first question would be: How would you fool it?
(IMO the item is tied to the makers "Soul", or gift. Your gift is different.)
You probably don't know the makers gift/soul well enough to duplicate it.
(ie: Real quick: Whats your best friends eye color??? Come on, faster... ...and thats something you look at ALL the time)
just my thoughts,,,
If you accept the premise that the talisman interacts exclusivley with the creator's gift, it comes down to the question of whether or not the gift is part of essential nature.
If it is, Hermetic magic can not affect it.
If it isn't, then I see no reason that a muto vim spell can't imitate another person's gift in the same way that a muto corpus spell could imitate another person's body.
Maybe , just maybe , this Talisman i found
is usable as an Arcane Connection when researching
this particular Muto Vim spell. 
Maybe, more likely this Talisman you found can be used in researching the Hermetic Breakthrough necessary to make that Muto Vim spell...
Ed
I'm not personally in favor of requiring research for this particular matter. Either hermetic magic can effect the gift or it can't. If it can, then I don't see why a muto vim spell could not be created to allow the caster to use the talisman.
Every time you decide that a particular trick requires a breakthrough or a mystery initiation you limit the range of abilities available to magi without that particular initiation or breakthrough. The spell guidelines are not comprehensive descriptions of everything that hermetic magic can accomplish. I think that changing your gift into someone elses is a task on par with changing yourself into a cat. It just isn't covered in the guidelines. (Of course if changing the gift is limited by one of the hermetic limits or some such thing then I'm wrong).
...Raven.. I wouldn't think you could use it as an Arcane connection....the Mage your trying to 'connect to' is dead...
(But he may not be in Heaven either. )
The possibility exists for the Spirit of the Mage to be summoned ,
hence the arcane connection.
A Talisman , apart from a Familiar ,
would probably be the most personal item a Magus has.
I'm assuming there is a distinctive magical aura of some kind associated with the Talisman.
You can sure expect the magus's sigil to be highly proeminent. Perhaps even manifesting spontaneously. Hmmm, what could the Founders' sigils have been?
Anyway, I don't really like the idea of people being about to make theirs another magus's talisman. Putting aside any in-game rationalisation, I feel it makes talismans less special.
I could envision a esoteric line of magi who can transmit talismans from parens to filius upon the parens death (how Twilight plays into that is discutable), but I don't like the transmission of a talisman to a complete stranger. And I would expect that line to put a particular emphasis on the "magical bond" between parens and filius (and there you go, an alternative House Tremere, complete with its very own Mystery).
Though a breakthrough might spread knowledge of this technique through the Order, I'd not let it affect existing talismans: they just wouldn't have been designed that way.
The suggestion is to use a MuVi spell to copy the aura , or imitate it.
Can you give me a Game Mechanic reason why this can't be done?
If you take the Talisman of a living Magus ,
you are guilty of a High Crime after all.
Sure , there are various Story reasons not to allow it.
Such spells are probably not encouraged as research projects.
As for a Talisman being designed not to be affected ,
there is nothing in the R.A.W. stating this to be the case , afaics.
They could include a ward to prevent unauthorized use ,
but this is a deliberate inclusion , not a default of design.
Say you were doing an adventure with a lot of Ghost Magi.
It might be useful to be able to use a found Talisman after all. 
hmmm not true. Would just mean that you cannot change it in any way permanently. By permanently I mean thru a momentary ritual because magic could sustain such a change indefinitely with the use of a magical device for example.
I would say it is possible. I would have the player investigate the object. he would have the choice of learning how to operate the object (learn new effects invested) or gather the essence of the gift of the dead magus.
A MuVi spell could then be divided to shround/twist your gift to resemble his for a time. I personally would make this a ritual to limit abuse.
Another way around it would be to simply work on a breaktru that would allow you to attune existing magical obj to become talismans. This is clearly a breakthru since it is prohibited in the core rule book. I would see it as a ritual that would break the current atunement & attune it as if you had invested the object. Then you would need to spend the season to attune the talisman to you.
Hope it help
All the Founders had the same sigil:
"Instill a feeling of awe and subserviance."
This sigil effect has
Duration: Permanent (unrepeatable breakthrough)
Target: All Magi (unrepeatable breakthrough)
Range: Earth (unrepeatable breakthrough)
It's not a question of fooling the talisman into believing you are its creator. It is a completely different problem from getting around designed-in usage restrictions. No "aura reading" is involved.
The issue is that the talisman is part of its creator. This is what enables it to affect him with Personal-range rather than Touch-range effects, as is required of every other invested device. You can also compare that to familiars, where the bond brings magus and familiar to Touch range. The familiar is not the magus, and conversely.
A magus that comes into possession of that talisman is not part of it. No amount of Muto Vim will change that, as it runs into the limit of Essential Nature. Those Personal-range effects which were intended to work on the magus rather than the device are completely unusable by anybody else by the talisman's creator, simply because they work at Personal range.
I believe the rules even say that the lab notes produced when investing powers into a talisman are specific to this magus and this talisman (Serf's Parma -- might have been about familiars rather than talismans, if not both). To me, this signals a much more fundamental design issue than 'restricted use': it is part of the reason why the spell even works in the first place.
In a similar vein, I don't think you can avoid being warped by "high-power spells not designed nor cast by you" simply by applying a Muto Vim effect to yourself to fool the spell into thinking you are the designed-for target.
Now, that doesn't mean you can't investigate and possibly reproduce them. I can't imagine Verditius not having a talisman worth spending years in investigation.
Just to point out that essential nature is not the limit here as it is the fabic of Mu spell's to affect the essential nature of things/effects.
After reflection, Talismans are odd things that do not work according to regular MT princeps.
If I were the line Editor, I probably would have created a guideline that said that if in the creation of the Talisman, the mage chooses to forgo the +5 bonus to all effect creation, the talisman could be attuned by another mage following the death of the original mage.
Two options would still be left.
1- The talisman needs to be passed at the death of the original mage
2- The talisman needs time to let go of this bond (Total mag of effects invested times number of previous owners = # of years before it can be reattuned)
Then again, I might, after considering the effect & game balance, decide to scrap the idea 
It would have added the fun of hunthing for legendary talismans. As the rules are & the intention I feel when I read all the limitations, is that with or without a MuVi spell, the talisman is only really usefull to his creator.
It affects things, but not their essential nature. That stays unchanged. A fundamental first step would be, in my eyes, to find a way to change what an arcane connection connects to. I am convinced that's beyond Hermetic magic. Look at the lesser limit of Vis (no Change The Nature Of Vis in ArM5), or that of True Feeling. These are two things I'd put in the same bin.
As I briefly alluded to before, this could make an interesting esoteric lineage, and a breakthrough worth working towards. But if you could just take a dead magus's talisman and make it your own, you'd see magi pushing their apprentices to create a talisman, murder them, put the talisman up for sale, lather, rinse, repeat.
I disagree. It is true that you don't get attunement bonuses and that some powers cannot be used. However, the loosened vis limit, along with the various bonuses still results in a significantly more powerful device than usual.
You can also expect a magus to be somewhat more enthusiastic about investing interesting powers into his talisman than he would otherwise be for another device. I would expect a number of them to be readily usable by somebody who gets into possession of the talisman.
If you want more, create your own. That is, I believe, the intent of the rules.