It will be hard for Paris Saint-German to win the Uefa Champions League trophy. Paris Saint-German has built its team around Mbappe, and if Mbappe is not in form Paris Saint-German will not perform well.
It cannot be denied that Mbappe's influence is quite big for PSG and if Mbappe leaves in the transfer this January then I am very sure that PSG's progress in the UCL will not be long.
However even though Mbappe is still surviving doesn't mean he will be able to lift this team's performance alone, I think PSG is not worthy of becoming UCL champions this season because we have to look at the strength of the team as a whole and PSG does not deserve that, especially this season their performance is very good inconsistent.
Mbappe acts as a driving force in the PSG squad, if he leaves it will cause PSG movement to stall. Maybe PSG condition is the same as Barcelona experienced when Messi left, the squad will lose direction which will result in the results obtained in the tournament.
Mbappe influence is very large at PSG, his departure will make it even more difficult for PSG to win the Champions League trophy. Luis Enrique needed several years to perfect the quality of his squad into a team that is ready to challenge in the UCL, this year the Champions League trophy is not for them.