Losing Mbappe I think it won't have much of an effect on PSG front line next season if their can get another striker at the later, PSG have lost messi and neymar but didn't make PSG collapse as a team, so losing Mbappe probably won't make PSG collapse either, and we're just waiting for time for them to get a replacement for Mbappe.
Mbappe was the most important player in PSG's squad. PSG's main scorer was Mbappe. And this team was also dependent on Mbappe as we saw. Hence, Mbappe's absence will definitely see PSG's performance deteriorate.
But Luis Enrique is an experienced coach. He will surely try to find someone suitable for his squad as a replacement for Mbappe. But we still don't know which player Luis Enrique will add to the squad as a replacement for Mbappe. Perhaps Luis Enrique will be interested in adding Osimhen to the squad. PSG's attacking performance is likely to stabilize if Osimhen joins PSG. Osimhen is a very talented player.