Losing Mbappe would cost PSG really a lot by the way. He is like their everything at the moment. In his absence I don't know how consistent and powerful PSG can be. They have made a good transfers for the future maybe but these new players will need to take their time to adapt and improve their skills to create a solid team.
In case of Mbappe's leaving maybe PSG would look for a solid replacement for him. But for now I don't know who they would go for. Maybe Haaland? Because his release clause is expected to be active by this year so we never know what PSG will do after that.

No one can deny that Mbappe is like the soul of PSG without Mbappe PSG's game is not so good but agree that PSG will find a replacement if he leaves but the time it takes to find a replacement will affect the team's game, but judging from his statement published on the account Fabrizio Romano's social media, we can predict that he will stay at PSG might happen, especially if PSG can achieve good things in the Champions League, PSG will try to keep this player.
https://twitter.com/FabrizioRomano/status/1742679156674965791Haaland to PSG? wow, that would certainly be very surprising, but is it possible? It looks like he will be a player targeted by many big clubs so competition in the transfer market will be very tight, and in my opinion, only club that a chance for Haaland to get many titles will be his choice.