When a club relies mostly on a player it is will be disaster for the club if the player leaves the club. I agree with you that since Mbappe is gone, it will be a problem to PSG to win UCL. I was thinking that the best time for them to win UCL was last two seasons when they had Mbappe, Messi and Neymar but it was still a floppy for them. Meaning, PSG might still be able to win UCL without Mbappe if they get a good striker and should not depend on only one player but they should get players that are capable of scoring goals. So that is the main player is being focused on in a match, the others can score making the players unpredictable for their opponents.
We are all quite curious about how PSG will restart their struggle in the Champions League without Mbappe, there is no worry whatsoever about their chances of dominating Ligue 1. It is indeed better for PSG management to change their transfer style, it is not necessary to recruit star players, but they should not waste their budget big for just one player.
It's true, PSG ever been built a star studded squad, their failure to win the Champions League trophy should be an important lesson. PSG management must proceed by building foundations, maintaining good transitions, and building a healthier environment within the team. Enrique is an experienced manager, he has won the Champions League trophy, and I am sure Enrique can lead PSG to success in the future.
Maybe at the start of the season, PSG's performance will be a little unstable, because they are used to Mbappe. Enrique must build new schemes and strategies to continue the struggle with other players.