I have a slightly different opinion than you on this. Even after Mbappe leaves, Paris Saint Germain will continue to win the French Ligue 1. But I don't think they will be able to find a replacement for Mbappe. Messi, Ronaldo, and Mbappe are special footballers. Paris Saint Germain, Barcelona, and Real Madrid will continue to win titles. But they need to sign players who are at least as good as them to recapture the glory of their playing days. Bellingham fits that description. That's why Real Madrid had a good season. But we can't say the same for Barcelona. Paris Saint Germain are very lucky to be in a league with weak competition. They will continue to win the French Ligue 1 even without Mbappe.
Not only Bellinegme have a good season, Vinicius was definitely no worse, so that’s the difference between them, Barcelona didn’t have such a strong attack, and they also lost Dembele, who helped Mbappe a lot at PSG.
It seems to me that any good striker will be comfortable playing in PSG, because there is very impressive support for the striker there. Remember all the forwards who played in PSG, each of them had a lot of opportunities to score, Ibrahimovic was also the best for this reason, and also anyone who becomes the new forward of PSG will score a lot of goals.