Losing of Messi and Neymar were never been issue for the PSG but now suddenly losing of Mbappé is going to be terrible for them even now I have feeling most chances if Mbappé decided to leave then management can sell this club as well because this will lose worth and surely need to be good amount for setting as par current standard, and they already announce few months back if they fail to fill their dreams they will sell this club so now most chances things will be gone in this way, and we will have completely new-look in next season which will be good for the French League because mostly teams will be on same level and competitions could be tough for the top spots as well.
PSG management will never allow Mbappé to leave this club as free agent so most chances these all things will be cleared in next few weeks with most chances in next season we will have PSG with all new faces and completely different side from this old era.
The departure of the stars (even if it's Mbappe) could be good for PSG - maybe they'll finally hire a head coach bigger than any of the players and we'll see not a bunch of stars but a real team.
And yes, I also think that after Mbappe's words, PSG will sell him this summer, but I don't understand how they can do this without selling him to Real (where Mbappe himself wants).