I haven't heard rumors of Dembele leaving Barcelona. But Barcelona will have to releas either Dembele or Griezmann. Griezmann does not want to leave Barcelona now and he has already announced that he is willing to reduce his salary. So I think Barcelona can sell Dembele.
On the other hand, I don't see Real Madrid as a title contender now. They have lost some important players in their team, new coaches in the team. Real Madrid have yet to sign a replacement for Ramos and Varane.
Griezmann's pay cut will not help Barcelona sign Messi. And this is the main task. So Griezman is better off finding a club and lowering his salary to move to another club. He has no other choice.