I was thinking that darn near none of the founders were explicitly dead and that bothered me. upon doing some research I see that the situation isnt as bad as I feared.
Bonisagus: left on a secretive mission in or after 836 and was not heard from again
Pralix: disappeared in 863, under suspicion of foul play, yet , suspiciously, she purposefully left the robes of dusty dawn behind when she took her last trip.
Jerbiton: Died in his sleep and is buried next to his wife
Bjornaer: Departed last instructions to her house in 831 then took the form of a giant bear and left forever (presumably final twilight)
Criamon: First founder to pass, sacrificed himself to become the axis mundi
Gurnicus: final fate never revealed. Wild rumors suggest that he found a path to immortality and waits for the order to fall just to say "I told you so"
Mercere: died and his body was cremated at Harco, yet some witnesses say that instead of his body burning at the cremation it was carried away to the hall of heroes.
Verditious: Was slain and had his heart removed as a result o a Corsican vendetta.
Merinita: Disappeared prior to 799 but people have claimed to have seen her intermittently since (1158) this could be consistent with the Guardian of nature mystery virtue. Alternately Myanar reported that Quendelon had bragged of killing her himself.
Tytalus: in 807 he left carrying only his staff with no familiar in sight. He visited every member of the house and spent a good bit of time with Hariste, then went of to win his heart's desire from the queen of the Faerie.
Tremere: died in 862
Flambeau: left his covenant alone in 820 for one final meeting with the Moorish wizards or alternately to live out his final years in a monastery.
Trianoma: Became a ghost. She's been haunting the forest around Durenmar since the top of her tower was blown off (but she unambiguously died in her sleep in 832)
Diedne: no information at all
Quendelon: disappeared in the mid 900's perhaps returning to Arcadia, it is entirely likely that he under went the ritual of Becoming and became a faerie
So for the fifteen founders or founder-ish folks we have only six bodies and of those six we have a ghost, a Genious loci, and a possible ascension to the hall of heroes.
In the category of "can be brought back for your 13th century saga to at least have a conversation without even the slightest disturbance of cannon we have 7 (Criamon, Trianoma, Tytalus, Qundelonm, Merinita, Mercere, Bjornaer).
In the category of apparently dead but there's no body so something could have happened we have 5 (Diedne, Flambeau, Gurnicus, Pralix and Bonsiagus)
That only leaves three, verditious, Jerbiton, and Tremere who died like men.
There was a point to this but I seem to have forgotten it.