Kuro: He probably won't return, but we might see some glimpse of him in the future. Maybe even a quick brawl with Usopp at some point.
Gin: He so have to return. After his promise and his badassness, he deserves a triumphant return.
Johnny and Yosaku: No, they won't return. They were just two very bad comic relief characters, who have no need to return into the story.
Wapol: We haven't seen him since Drum, so why should we see him again?
Bellamy: Same there, haven't seen since Jaya, he is presumably dead, so no.
Enel: Oh heck yes. Enel will have to return to earth with his Spaceys at some point right? :wub:
Foxy: He will probably return in a filler anime arc, since that is his destiny it seems.
CP9: Hmmmmmmmmmmm no.
Morgan: He will probably face off against Helmeppo at some point, and Helmeppo will of course beat him.