Not only is it difficult, it seems impossible. Mbappe was PSG's biggest trump card on the way to the championship every year by smashing the statistics. They lost this trump card and Mbappe will continue to work wonders in Real Madrid. Mbappe's absence will leave PSG in a very difficult situation. No matter who is replaced by Kylian Mbappe, he cannot perform like Mbappe.
This very true almost everyone knows that mbappe was a very important and key player in PSG such that in some games they literally depend on him to be able to win games or even get to score goals and so his exit is going to bring about some set backs within the team until a good replacement is gotten. I don't think anyone is really irreplaceable in football els there wouldn't have been opportunity for these younger generations to be able to do as much as they have been able to do in this era of football, some young players now have even done more than the former starts did.
Most times when a good player leaves a team it's usually normal to think the team may begin to crash as they may find it difficult getting a new player who will perfectly replace the one who just left but then later it turns out the team gets to cope for awhile and eventually gets to makes for the absence of that plyer such that they are not affected too much any longer. Just like Madrid when Ronaldo Left it felt like Madrid was not going to be any better but it turns out that they are now a good team such that in the whole of Europa they standout a d same can be the Faye of PSG if they focus more on grooming their players than looking for Stars to buy.