Can you bond longevity rituals to your familiar to evade the warp accumulation?
No.
In game, a Longevity Ritual is not an effect to be invested in an item, and thus cannot be invested in a familiar bond.
In meta-game terms, making Hermetic magi immortal is a bad idea.
Plenty of other forms of Warping (Divine Ascent, Fatra Bayna; Natt'Thel if you don't mind being immortal without magic) to choose if you want immortality. 
You can also bind effects into your Familiar that improve your quality of life - always ensuring that you have fresh air around you, personal wards against demons of disease, ReCo effects to balance your humors, stamina increases, etc. Such effects can functionally act as a sort of no-warping Longetivity Ritual that (unfortunately) doesn't have botch resistance. (Plus, invest in a personal physician and an ultra-swanky lab.)
So basically you can go that route, which works for your first few Decrepitude points. After that, you should probably start using the Longetivity potion.
If one were to tie their Longevity Ritual to their familiar somehow, what would happen when the familiar dies?
Rule-wise, I'd argue that the LR is just no longer active. The effect just doesn't exist any more. I also wouldn't put up a fuss if another SG ruled that the LR remained active but now began to Warp you, though I wouldn't rule that way myself.
Given the fluff of a familiar's death signalling impending doom for its master, however, then depending on how the player in question felt I might have all the age and/or Warping pour into them at once, almost certainly killing their not-LR-protected self the second they got done with their Twilight unless they comprehend it and gain the Transformed (Being) Virtue or something. Either way, their time as a living human will probably be short.
Well, a familiar can also suffer from a violent death.
Just max out your bronze cord, that helps with aging rolls the same as a longevity ritual, and without the warping.. Of course it has a max value of +5, but that's not a bad LR...
Yes, yes it is.
+1
+5 Bronze cord also eats up a lot of the bond, perhaps all of it...
+5 would be a good LR for an under-50 magus, to get 15 free years without warping and, if so inclined, 10 or 15 more years to make children with, but no magus under 50 is getting the kind of lab total that requires. The Bronze Cord is most useful as an adjunct to an existing LR; it's not like the Solomonic Magic Defenses where you can go "lol aging" until it's time for another dose of Al-Iksir.
Depends upon whether you can convince the SG that the familiar bond falls within your focus, too. I have an overspecialized weather maga with a Golden Eagle familiar, she bound it with a lab total of 52 (she can strengthen the bond to 67 now, given she gets the assistance of her familiar where she didn't before) and could have had a +4 bronze cord. So, +5 by 50 could have been possible had I put everything into the bronze cord (+3 bronze, +2 golden, +1 silver), getting to 5 now would require another 45 points in lab total to strengthen the bronze cord. She's within striking distance of +4, though, her Arts have increased, and she can now use her familiar to boost the lab total which she couldn't use before.
I emphasize the "under 50," though. Going by this, you want at least +3 by 35 if you're going for an extended youth ("youth," for a magus, means "before the longevity potion"), which means you'll get some Aging Points but likely not enough to hurt anything (it's the kind of thing family-oriented magi, or magi who're okay with a bit of age in exchange for fewer Warping Points, might do).
Now, for an absolute twink-out, you can do Strong Faerie Blood and Bronze Cord 5 by 50, which gets you -8, which gives you absolute safety until 60 and practical safety (see above, and also counting living conditions) till 110 without an LR, better with regimens (in theory; in practice, don't waste your time), and also means that once you get your Longevity Ritual, you won't age at all until you step into Final Twilight.
Ramidel, you initially said that no magus under 50 is getting the kind of lab total that a bronze cord +5 requires. It is possible for specialists with a focus and who can bind their familiar under that focus and if they favor the bronze cord over everything else. My particular maga did favor the bronze cord, but not to the exclusion of everything else. If she had (made bronze cord +4), she'd only need a lab total of 75 to get to +5, and right now she's at a lab total of 65 and is age 34; she could easily get to a lab total of 75 before 50. However, she has Master of None, which makes it a bit more difficult to ratchet up Arts as quickly as possible.
There are other places to get bonuses as well, but I was sticking with familiars. If you optimize a lab for binding familiars, or for the arts you will be using... there are lots of ways to get that lab total up as well, and it does not have to be creo+corpus- a mage who has problems in one or both of those arts might find it easier to build a familiar bond than a longevity ritual.
a +5 bronze cord requires a lab total of at least 75. The same +5 bonus on aging rolls requires a lab total of merely 21, or even lower if the magus is willing to toss in an extra pawn or two of vis. It's challenging to come up with a set of flaws that could lead to a 54+ point difference in lab totals.
The bronze cord helps some (I saw that with the Adelbert thread it was a lifesaver for him), but it isn't anything close to a substitute. Now a moderate bronze cord combined with a longevity bonus from skilled cooks/bakers from city and guild, an excellent covenant living conditions modifier, and a physical regimen by a skilled doctor from Art and Academe would allow a magus to live for a long time sans longevity ritual at the cost of lots of wealth (and of course they all stack with the longevity ritual so you can't do "better" than hermetic longevity with these four bonuses because you could always do all five).
On a different subject doing all five (and stuff like sayoshyant's elixir or longevity of the forest) is why I don't see unageing sahir as a problem with the setting. The difference between I can live forever until something kills me and I can live up to 370 years or until something kills me is more or less negligible because my mythic Europe is at least somewhat dangerous.
Puissant + Affinity in non-Creo non-Corpus Familiar-appropriate TeFo, a Magical Focus, Deficient Corpus, and Difficult Longevity Ritual probably gets it. If it's not enough, it's not a stretch to interpret that Deficient Technique and Deficient Form stack, in which case there's Deficient Creo and go ahead and put those Puissants and Affinities back in CrCo and you still probably won't even manage a +5 or higher LR.
It isn't THAT hard.
@Jonathan.Link: Fair enough. So yeah, if you specialize to the max, you can put in some extra years before having to get your ritual.
@Erik: Also, if you use Sihr like most sahirs, getting spirits to become your Al-Iksir is not trivial unless your Sihr is very strong (an Ease Factor of 36 for a ten-year ritual, assuming the standard offering). Of course, it can be made easier if you have enough vis, but for a sahir, there's no such thing as "enough taqa."
More like 5/7 specialized (don't have Puissant or Affinity Creo), and perhaps a bit less when you factor in Master of None. I've focused on improving her Creo score post gauntlet, but can only do that once per year.
I think this Bronze Cord 5 thing is being examined the wrong way for longevity because of the term "longevity." If we look at longevity as extended lifetime as a magus, we should consider Final Twilight as well. Gold Cord 1 & Bronze Cord 5 loses out to Gold Cord 4 & Bronze Cord 4. You lose 1 point for aging rolls and 1 point of Soak. But you get a 3-die reduction in magical botch dice, which is hard to get and can significantly reduced the number of warping points accumulated and the chance of even entering twilight (which causes even more warping). Let's say you get exactly 75 for a lab total for your familiar and 21 for a longevity ritual. I suspect you'd end up with far fewer warping points and just as much aging protection choosing Gold Cord 5 and a 5th magnitude longevity ritual than you would choosing Bronze Cord 5 and forgoing the longevity ritual.