PSG does need new players to replace Mbappe but they don't have to get players who have equivalent performance to Mbappe.
Now we can see that PSG doesn't have any problems winning the league 1 title even without Mbappe, PSG will still dominate league 1 just with the existing players and that's all because the players that PSG has are of higher quality compared to other teams.
Bringing in Rashford or Osimhen will not be that easy when Napoli and Manchester United are both in bad shape and need help from these reliable players to get good results in the next season.
I think PSG will not be able to get Rashford or Osimhen this season or may have other alternatives.
If PSG's target is only Ligue 1, of course even without signings like Osimhen and Rashford they can still dominate the league. but if they are targeting something bigger like the Champions League, of course it will take a bigger effort to get a replacement for Mbappe. and it seems that currently what PSG is trying to do is bring in big-name European players.
Let's see how Mbappe gives his best performance for PSG this season. he will go and he will provide great memories for the fans.