I haven't seen much about Sam Winchester in the general tag lately, so here's my speculation on his ending.
I rewatched 15x4, since Becky's figurine set up was supposed to be foreshadowing and realized I hadn't actually listened to Sam the first time watching (shame on me).
He mentiones a few times how people get to live their regular lives without knowing what's actually out there and he sounds just so bitter about it, almost pissed off, but in a hurt way.
When Dean tells him at the end of the episode that they're free ( which he thought at the moment), Sam says he doesn't feel that way, that he feels trapped and is still thinking about Jessica and the things they had to do.
So Sam basically confesses he's to ptsded for a normal life.
At the end of 15x19, when Dean, this time correctly, states they're free, Sam's smile seems forced and he's close to tears.
So I'm absolutely convinved at least Sam will die. I of course hope, both brothers will and maybe meet up in heaven with characters that haven't been brought back by now, maybe via Ash, I'd love to see him again. (Interwiews always stated special chars will be back, but a lot of characters have already reappeared in one form or another during season 15, which only leaves dead ones).
If Cas comes back, it will probably be as heaven's new manager or the new death, that way he could interact with the Winchesters again once they die for a short reunion, which wouldn't take away from his ending in 15x18.
As a Sam!girl I would like that ending. He needs to rest, be truely free, he wanted that since season 8.
(Same goes for Dean, who's been powering through with a fake smile since season 7, but I don't trust Dabb to give me a brothers ending...let's see how it goes...).
