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.
Mbappe is the heart and soul of PSG including the Les Bleus, the pride of France. And for that reason, Luis Enrique and the Qatari owners are keeping their hopes alive.
It appears impossible to bring Haaland to PSG but doable. Mbappe rejecting PSG once more, the club will also become more aggressive in its pursuit of a replacement. PSG is a luxurious club, perhaps number one in Europe. PSG will match any of the best clubs on the planet. In the event that the most ideal decision of Haaland is to come out on top for championships of EPL, the best league in Europe and the Champions League, staying in Manchester City is the ideal fit to him.