When it comes to 3rd parties in Smash, I see Sonic, Pac-Man, and Mega Man returning for sure. Sonic is pretty much a mainstay at this point and Pac-Man stays as long as Namco is there. Mega Man... I think Capcom is buddy buddy with Nintendo so it should be fine.
To that extent, I can imagine Ryu and Ken staying as well, or Ken goes and we get Chun instead. Kazuya I can see retuening in some capacity, Bayo is basically a Nintendo character at this point so I can't see her getting the boot. Idk on Joker, they may want to promote the newest Persona game instead.
Squeenix I think will come back as DLC, though FF is weird cause the music is in copyright hell, so I can see Sephy gone. Hero pribably is DLC (possibly base game), Sora probably returns as DLC as well.
No idea on Konami characters.