Khel Hellam dying and being replaced by Jinsung would be cool. I expect he'll show up with the FUG cavalry. Someone mentioned that we knew that the FUG elders and Sophia were on their way - I know we've had confirmation that they're interested, and from a storytelling perspective it's obvious they'll show up, but was it confirmed somewhere I didn't see that they are en route?
As far as casualties on each side go...
I agree that Khel Hellam is a likely sacrifice on FUG's side. As someone else stated, his main ability has been thwarted multiple times by Zahard and this whole arc has been tightly related to his origin story. He's also one of the strongest characters we've seen thus far (him fighting Yama and Evankhell simultaneously becomes more hype as we see what beasts both of them are on their own) and I'm expecting that if he fights anyone it will be Lyborick.
Cha is definitely doomed to die in the course of this story, but I expect it will be farther down the line. He hasn't even really been fleshed out yet as a character. I expect that if the 8th Son shows up, Cha and Dowon will get a rematch versus him.
I don't expect any of the Baylord brothers to die, but honestly, if any of them did I would expect it to be Doom. They seem like they're part of the squad now though.
Evankhell's death flags seem to have passed. I also expect Evankhell to die at some point in the story, as it's been pretty heavily foreshadowed that their destiny is to go down fighting, but I'm not sure if it will be here... I could envision some sort of situation where Zahard hits the Delete button on the nest and sends in Adori or something and Evankhell burns out bright to hold off Zahard's army while FUG escapes with Jinsung. It would play nicely into the idea of Baam saving his teacher at the cost of another, but IDK how much SIU cares about that sort of thing.
On Zahard's side...
Yasratcha is doomed. Yama is going to destroy him savagely this time around. I'm sure it will be a struggle, but he's just not making it out of this battle alive.
Kallavan's role in the story also feels like it's ending. He's too much of a zealot to betray Zahard. I expect he'll either try to kill Lyborick once he escapes his current predicament and be slain to hype Lyborick as absurdly powerful, or else he'll get his revenge and end up killing Lyborick later on and possibly die in the process.
That said, Lyborick is also definitely going to die at some point, but it isn't clear to me if it will be now. SIU might have plans for him to develop into a recurring villain. I wouldn't be surprised if he ends up dying though, I think the Nest will be a victory for FUG and if Lyborick was hand-picked by Adori he seems like the type to go down with his ship. The whole flashback with Hund Lych Khun also debunks my previous hypothesis that he could be a deep plant for the Poe Bidau family - he seems absolutely loyal to Zahard.
Maschenny is definitely not going to die. I hope we get to see her fight though.
After the Nest battle, it feels like the LPB family's standing will be severely debilitated. They've lost two of their strongest family members so far, and it's safe to say several more are going to die as the battle continues. The Nest is almost certainly going to be conquered or destroyed by FUG. I also noticed the LPB family head is most likely the lowest ranking of all the 10 Great Families, and it wouldn't surprise me if he ends up being one of the first Family Heads to actually show up in battle against FUG later on in the story.