As for Steph, I don't think that the Warriors will let him go and the same goes for Luka. Although some rumors about Steph and Lebron teaming up.
I think that we'll never see such thing in the nearest future. And for KD, he's known for that so when he's done with the Suns, he'd move elsewhere but where?
Yeah, I'm not seeing Steph leaving the Warriors, he could be just one of those few players that will finished their careers with the team that draft team. And there is no need for Steph to go out and try his luck on free agency.
He had build the Warriors dynasty already, and that is good enough for him to cemented his legacy with them. And with his performance in the recent Olympics, Steph already put his name on top. Giannis? perhaps, as we can see the frustrations in him when they exit the playoff. Luka? he is still trying, and with Klay now with Dallas, he will go out for another championship run.