Since Messi has left the team, Mbappe is now the main player in PSG's squad. The team will now depend on Mbappe's performance. PSG management is well aware that now Mbappe leaves the team and their performance will drop badly. They will even lose dominance from Ligue 1. However, PSG has another star player Neymar in their squad. However, due to injuries, he could not stay with the squad for the full season. And so PSG will not risk relying solely on Neymar. Next season we will likely see both Neymar and Mbappe in PSG's attack.
Mbappe was PSG's main player before Messi, during Messi and after Messi's departure he remains the main player. And it seems that your prediction is in danger of being completely wrong: PSG are forced to sell Mbappe, and PSG want to get rid of Neymar. Most likely, both of these players will not be in PSG next season, but I don’t think that even taking this into account, PSG will lose their dominance in Ligue 1.
In several seasons after the 2018 World Cup, Mbappe has proven his playing skills, even when compared to Messi, Mbappe is superior.
As I expected that PSG will release several players in attack but as for Mbappe I still don't believe that PSG will let him go considering he has become a core player there.
By releasing Mbappe's departure, wouldn't it actually be able to bring PSG in difficult times because the player they relied on had left there.
Indeed, PSG is like an authoritarian club where they can arrange everything they want when they have got the players they want and it is evident that most of the players who have left very few have sweet memories with this club. It is clear that when things don't go according to PSG's wishes, most of the players will feel uncomfortable and that is what Mbappe is currently experiencing.
It is very clear that Mbappe has made a statement that he will remain with PSG until 2024 when his contract ends, but PSG will still insist on selling him because of course PSG will lose big when Mbappe changes his status to a free agent in 2024. I hope PSG will experience difficulties in the next season if they will be left behind by all the key players and in the end they will sink because they put too much pressure on these players.