Nobody's ever gonna leave considering the Tokyo team has experience and now the aliens are attacking common people, newcomers don't have the knowledge/strenght that they currently have. They must stay to protect the innocent people that will get killed during the upcoming missions.
Anyway, most of them don't have enough points and there's no way they'd prefer getting slaughtered IRL then fighting their asses out for everyone's life.
That's just my two cents... imo most of them will try to get a weapon upgrade, even Takeshi the day he'll have 100 points... I can see him stayin' in Gantz to protect people, just like Kaze did for him.