For me, PSG's dominance will end when Mbappé leaves, I know that they feel safe with the player, and in fact they do, but basically when we can think about what they can do and achieve, well for me it is a fact that the only one who moves that team is the french, and he doesn't understand it, due to the whims of the player in the team he already has everything, he is the only leader, he already ran to messi and neymar, that was not what he wanted to, ? According to Ney, the player was too egocentric and he only had to do things the way he wanted them, and if they were not done that way he would basically make them leave the club, so this player cannot be given much power, if he goes to Madrid I am sure that he will not succeed with his whims, because the players there will not do what he likes, things are different there.
PSG is able to dominate League 1 because of the contribution from Mbappe so that I will have the same opinion as you that PSG will begin to decrease its performance if it cannot find the right replacement to replace Mbappe and Mbappe departure from PSG can be said to be a big disaster.
maybe everything will change when joining Real Madrid but believe me mbappe is very selfish but if he thinks about his career he will definitely be a solid player to other players to create strong troops to win the prestigious title in the coming season.
Mbappe, I think he will have relationship difficulties at Real Madrid, there he will not be the big star, but just one among other stars and will have to share all the attention and spotlight... All the strange behavior he had with PSG during the negotiations and everything he did with his PSG teammates. How will he deal with this? I'm even curious to see how his season in Spain unfolds.