It is Ligue 1, it is not the Premier League. PSG should under any and all circumstances still easily win the title. It is too one sided in that league. PSG has got billions backing the team. No other club comes close to that. And it is not like Mbappe leaves an empty space and they play with 10 men only. Someone will fill the gap and they have several top players sitting on the bench most of the time. There is a chance that several other players now thrive and become much better exactly because Mbappe is gone.
The difference in quality of the league sometimes determines one team can dominate so easily and for example we can see how PSG can be one of the strongest teams there. Moreover they have very good finances so they can buy any player they want even though the overall quality of the team is important in a team to achieve success. Losing Mbappe will not be a big problem for PSG because they have several other players who can fill the void in the position left by him.
For Ligue 1 I don't see much difference and PSG will still dominate. But what PSG need to think about is how they can compete for the Champions League title. This task is considered quite difficult and Luis Enrique has a big responsibility in delivering success in the Champions League.