No new groups
I dont think this story will be restarting soon or at all, personally I believe this group of people is the last group and they are getting closer to the main group of enemies and we'll be finding out more about Gantz soon. Also the truth has been seen by the public and all points lead to the end of the series. But I may be wrong ^_^.
I belive u are wrong cause there are still the:
what did gantz ever do to vamps question
the end of the world question
and the return of Tae,Kato and kishimoto + the super weapon
we sill be seen Gantz for a long time
there are more people comming into the room but they die easy and I belive that gantz have a limit on how many people can there be on a mission so In that part yes this can be the only group of players we will see for the time be untill they start to die
I don't think the whole team will die, I think this team will now start trying to revive those they can and start to gain their freedom. With this they will be facing off with the vampires soon and after that is the eventually clearing up with the mysteries.