Yes, the departure of Messi can rather be considered a relief for PSG. By the way, like the departure of Neymar, but there is still no certainty with him.
As for Mbappe, in my opinion everything has already been decided, but now there is a bidding process Real wants to get Mbappe for less than 250 million (quite reasonable given the remaining year on the contract), PSG, on the contrary, is trying to get as much as possible, like Mbappe who pretends to be ready play another year at PSG.
Neymar there is still no speculation regarding his departure because so far no official offer has come to PSG for Neymar. I think it will make him stay longer with PSG because he is not in a hurry to leave PSG because he has a bigger salary at PSG. Mbappe is also reportedly ready to be released by PSG if there are interested who are ready to pay the price they want. Apart from that, only Real Madrid is often associated with Mbappe and no EPL team is really serious about getting Mbappe at 250 million.
In fact it was like that where Mbappe seemed to pretend he would choose to stay with PSG but on the one hand he rejected a new proposal from PSG. So there's something else going on between Mbappe and PSG management and I think he's starting to feel uncomfortable at PSG.
Neymar has no interest in leaving PSG. Because he gets high wages at PSG. And no other club will be interested in paying Neymar such high wages if he leaves PSG. The main reason is Neymar's fitness is not good. Halfway through the season, he was sidelined with an injury. No top-tier team would recognize such a player and pay high wages to keep him in the squad. Neymar will remain at PSG until the end of his contract with PSG, after which he will either retire or join a club in Saudi Arabia.
PSG management is not interested in letting go of Mbappe. Mbappe is not renewing his contract with PSG. Even so, I'd say PSG management will continue to do their best to keep Mbappe in the team.