It is difficult to imagine PSG performance if Mbappe left them, even though they will still dominate Ligue 1, it will be very difficult for them to win the European Champions League. I think this speculation will be answered next season, when the transfer market opens and Mbappe will decide his fate.
Cristiano Ronaldo and Leo Messi era in Europe is over, verge on new comparing energy from other upcoming big names. Transferring Kylian Mbappe to the English Premier League would be an unwise choice because he needs to anticipate in league where he will be valuable to a club and enjoy his football pattern other than some competitive EPL clubs that don't care about him other than giving him stringent regulations to follow and criticizing him when he's injured. Apart from the fact that the EPL is not safe for such significant players, his opponents would aim to pull him off the field by injuring him. Kylian Mbappe is a big name in Paris Saint-Germain, and his presence is important to the club.