Gunn loves Rooker (and making fun of him) so I would imagine he becomes a Starro-zombie at the end. Boomerang famously survives every incarnation of Suicide Squad and the fans really want him to survive this movie but I feel like Gunn will kill him just to say f**k you. I mean the tagline is literally "Don't get too attached".
If I had to bet money I'd say Harley, Peacemaker, Bloodsport, and Ratcatcher survive till the end.
Mongal, Blackguard, TDK, & Javelin almost certainly die in the opening battle
I've got a feeling he is going to make Polka-Dot Man one of these tragic characters we all come out of the theater loving.