Mbappe is a very special player. His place will not be easily filled. There will be very few players who can achieve the success he achieved. If Mbappe had left two more seasons earlier, Messi and Neymar would have been more important players. But Mbappé is the key player this season. Mbappe's absence will affect PSG badly, but Enrique is certainly thinking about it. I think he has already chosen the player to replace him.
Even though it is not easy to fill the position left by Mbappe at PSG, Enrique still has to think about this for the sake of his squad next season because PSG will have to fight even harder next season due to not having Mbappe in their squad anymore. But just to compete in Ligue 1, PSG is still the best even though Mbappe is no longer there, but the problem is when PSG plays in other leagues such as Champions, which will make it more difficult for them to compete next season.
No matter how special a player is, of course his position will be easily replaced by other players later, players of the same class as Messi and Ronaldo can currently be replaced by other players, especially Mbappe whose quality is far below Messi and Ronaldo in my opinion, Mbappe has been a very talented player and of course we admit that, but we also don't forget that Mbappe's success so far is also inseparable from his status as a PSG player, previously Mbappe was an ordinary player when he was in Monaco and two loans from Monaco to PSG at that time did not show Mbappe's good performance because he was covered by Cavani's prestige as PSG's main striker, but after Cavani left, of course Mbappe was able to show his talent at PSG after getting one main place and supported by other PSG star players for him to score goals during this time, so I think, if he was still in Monaco of course I doubts if Mbappe will be able to become what it is today.
Leaving and coming a player at a club is of course commonplace, so I think PSG will not be too sad with losing Mbappe at this time, because indeed with the finances that PSG has, of course it is not difficult for PSG to get a replacement for Mbappe later, so indeed we just have to wait and see, if other players will replace Mbappe position in the PSG squad next season.