The most supported outcome is eternal comaland, actually, because Lisa mentions taking care of someone a few times in Ward. Though it's ambiguously worded enough you could interpret it like something else, I guess.
edit: well, she outright said she's taking care about Taylor, iirc, but if you choose to interpret it as tending to her grave or making sure nobody finds her, then be my guest, I have nothing against it.
edit2: I had to reread some parts of Worm to confirm it, and I hope you appreciate my sacrifice, lol.
But okay, in 27.1, Taylor figures out by Lisa's expression that her dad is dead after the Scion's attack. Lisa doesn't contradict her.
So him popping out in the epilogue is either a miracle or a readily apparent contradiction.