Indeed, we don't have confirmation of who is still in the trust system for 81-90 dungeons, other than Estinien, so its entirely possible that someone could be killed off between the last 80 dungeon and the start of Endwalker.
The Twins are very unlikely though, and so is G'raha as we just got him and he's had enough death fake outs as it is.
I'd however put my money on someone like... Matoya.
I think Sharlayan is the next big area they'll be announcing in the May fanfest event, and so with a Sharlayan heavy plot, with more chaarcter development for the twins and the scions as a whole, Matoya or maybe even Krile could be on the chopping block.
