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.

There is no way Haaland would want to prefer a move to PSG,he would rather stay at Mancity than move else where.Mbape is very eager to make a move from PSG to either Madrid or any north London club,I heard he was looking at moving to either Chelsea or Arsenal,but I think he would still stay at PSG because he is currently playing in the champions league with his team,and he wants to win the trophy with his club.
Haaland is a big player and his contribution to the Manchester City squad is one that they can't do without, therefore, contemplating on a move to PSG is not even in his plans.
Unlike you think Haaland is actually quite likely to play for different teams as well. At least his father said this before when people were talking about the hidden release clause on his contract to be active in 2024. But would this happen this summer? It is hard to predict that for now. Maybe Haaland would like to stay for at least another season as well.
But I think Manchester City won't be the only European team in his career after leaving Dortmund. As long as his release clause is paid Manchester City can't do anything to prevent him from leaving. It would be up to his choice.