If Griezmann leaves Barcelona at the moment and joins Atletico Madrid, Barcelona will have no problem. Barcelona now have plenty and extra Strikers.
I've seen a few new players come in in the friendlies so far and it look like they're good enough to plot as regular throughout the 2021/2022 season. Yes, Barcelona have an extra striker next season so it would be safe if Griezmann returned to Atletico.
Barcelona may be planning to release Dembele or Griezmann. But I was saying that Atletico would be stronger if Grismann will join. And next season Real Madrid is forming a very weak team compared to the previous season. So with Griezmann in the squad, Atletico Madrid's chances of winning another title will increase.
Dembele wants to be released? I'm not sure about that and so far it's still a rumour. Even I'm not so sure Griezmann will leave Barcelona to return to Atletico and I'm sure he will stay at Barcelona. As for the chance of winning, I firmly believe Atletico will not be able to defend the La Liga title last season and reclaim it next season. Barcelona and Real Madrid are tough competitor for them, and I feel that if it's not Barcelona then Real Madrid will win it next season.