100% dead
Kingdom Come Supes: A Supes has to die.
Flash 90: See above.
Every guest from another earth (Conroy (?), Birds of Prey, Burt Ward, Smallville): Vaporized, only one earth will survive or they will manage to fuse the few remaining.
Pariah: Don't see him come back, he only has been useful for the crisis setup.
Harbinger: She has gone too far to come back (and as the show is ending, Arrow characters are the most likely to bite the dust for real).
Monitor: Dies as in the comic book. Most likely, in ep3.
Anti-Monitor: Bad is dead.
Kinda dead
Oliver Queen: Ok, the controversial one, seeing everyone here. He will have his "sacrifice", probably in ep5. But it would have been stupid to do the Felicity 2040 final scene if he was truly gone. He will take the Earth 2 Supes place in the pocket universe and enjoy his retirement with no way out.
Barry Allen: Going for the sacrifice, saved by Earth 90's Flash, stuck in the speedforce. Come back an ep or 2 after Crisis, for drama purposes.
Iris and a shit ton of other non-hero characters: Vaporized in the trailer, either going for a time travel heist for the remaining infinity stones with the Legends or another way to bring back all the dead.
The ending of ep3 will be a "we lost" cliffhanger. I can see most of the deaths not stick, outside of Arrow characters or guest stars. It won't be the first time they use time travel to repair the damage after a "shock-value" moment.