Short questions, a covenant has every mage member perish, and become for all intents and p's ghosts which are not only self-aware but can even teach.
What is their status in the Order of Hermes, specifically the Theban Tribunal?
Do they retain any right to their covenant, property, or status?
From Mysteries, Revised Edition in the section about Living Ghosts (specifically page 70).
Note also that one's protection under the Code of Hermes nominally ends at death; while he may retain sympathy and friendship with his sodales, all Hermetic status and legal protections are immediately lost.
This may well vary by tribunal, too. I'd have to check a lot of pages to see if there are other notes on this. Does GofF have something on this?
Chris
Depends, of course!
Normally, a dead magus has few (if any) rights and his property is inherited by his heirs, and where there is ambiguity/conflict about who those heirs might be, then the Tribunal will decide (or perhaps Wizard War or Certamen will decide).
However, it all depends on context.
Are the ghosts known to be dead? Are the ghosts claiming to be alive? How many political allies and enemies do the ghosts have (which will influence any Tribunal rulings on their case).
Generally, the Tribunal should have Peripheral Code guidance on what to do in such circumstances. Afterall, many/most magi "die" via Final Twilight and that is an ambiguous event; which is only "Final" because the magi have not come back yet.
Not in so any words (that I could find), but since the dead are still considered voting members of the Order, I'd assume they'd retain property rights.
Thus playing merry hell with inheiritance obviously.
Ah, that's the part I was vaguely recalling. I don't recall anything specific for the Theban Tribunal. But clearly things can vary a lot from the general rule of thumb presented in The Mysteries.
Chris
You sound like a disgruntled Tyro from Rhine Tribunal, don't you? 
But Rhine Tribunal does not give voting rights to the dead - it rather accepts to err on the side of caution when determining final twilight of valued and often irreplaceable members, and allows their sigils to still be used by responsible younger magi, always in the best interest of those whose fate has not been satisfactorily determined yet. 
Sodales who consider this caution exaggerated tend to be cupidi rerum novarum who dream of a Lotharingian Tribunal.
Cheers
I'm not sure what rights such a ghost would have, but it would still have obligations: the Code says, 'I, Bonisagus, hereby swear my everlasting loyalty to the Order of Hermes and its members.' I take it that this means that a Magus' duties under the Code do not end at death.
This is such a fantastic can of worms that it's almost invariably going to result in some story of some form or another.
Regardless of what 'rights' a ghost has, there will always be others who disagree. There are a lot of things that tend to expire upon the death of a person (marriage, for example) - and because there are a variety of precedents there will be a variety of interpretations. As Richard says, it's going to come down to who has the right allies and support network. All's fair in love and Hermetic politics.
What I tend to use for my tribunals/charters on ambiguous death/final twilight is that if a person is absent for a period of 49 years (7 tribunals), they are assumed to be not coming back and their stuff is passed on to their heirs. If they pop back in the following year (50 years!) then the recovery of their things is their problem.
That's the fantastic thing about Mythic Europe: final twilight can claim someone ambiguously, but so can a walk into the forest followed by a clandestine mugging and burial in a shallow grave. Death is such a fantastically ambiguous thing in Mythic Europe! Estate Management Law must be even more of a nightmare than usual... 
Thanks so much everyone for the replies. Of course what you wrote Richard really sparks inspiration in how to move forward. As it stand the ghosts are each magi which only just died after being betrayed. The covenant is a winter covenant which had very old and modestly powerful magi, but now they are dead. Their ghost exist in this very odd regio which is a dream of the giant Polybotes.... long story. Anyhow the ghosts of course can move about some within the covenant, but can only truly manifest in the regio.
The players are characters that arrive to attempt to save the old magi only to find success elude them and the covenant members perish. A convoluted and complicated story which I perhaps did ill justice to, but I had fun running it so there we are.
As a response to your questions, I now am inspired to lead the way in our troupe to answer these and other problems that the story embodies. We truly will enjoy gaming out just what happens when the "dream ghosts" try to barter on their old allies, and what happens when old enemies learn that their foes have vanished one and all. I am sure it will upset the Theban tribunal for years to suddenly have five very stalwart and powerful magi die, but still be present so to speak.
Thanks again for all the replies. Truth be told while it may be a great story in the future, it is certainly one that will require a detailed and attentive SG with skill beyond my own to truly give it the powerful performance it deserves.
The way we become great Storyguides is by challenging ourselves with great story ideas. Start slow, and build. 
True. Very true.