I doubt Wario would die (It would piss off a lot of people) but with that I agree most of the villains may die (Mainly Decious or Darkness, Bowser and Ganondorf would probably be defeated and return to their respective worlds to continue their own thing.)
Ken and Ryu would probably patch up things and Pauline would forgive Mario (Let's not forget she's probably brainwashed by Nox Decious so she isn't really evil)
I hope they don't have every villainous characters die.
Ganondorf would probably be weakened and maybe Sage might make an appearance to help seal Ganon in a sacred realm or something. That's my theory for Ganondorf's last appearance.
Characters that are not original are either going to be defeated (but not killed) or flee the war.
I theorized that Pauline is probably cursed by Ganondorf to embrace her darkness in her heart which is to hate Mario. Who knows, she may not want to harm DK. So it's likely she'll live since she's a part of Mario's love triangle where people can argue if it's Peach or Pauline for Mario.
Scott is an original character so he can either live, be stopped, or become deceased.
This Finale will be awesome because we don't know what their idea is mainly on.
If a hero were to die, I don't think anyone on Mario's side would die since they are not original.
Mona may have a close connection in the series which is what I hope for but still live in the end making Wario the longest to have a girlfriend and possibly get into a deeper relationship. A wedding episode! Who knows.
Here's an idea which Richie may not see!
Like that's ever going to happen