Mbappè is rumored to skip the second leg game with PSG.
If this will be the truth I think PSG will have a very low chance to beat Manchester City with a useful result.
Remember they need to win with 2 goals advantage in England not an easy task without their best player.
Mbappe is important for PSG but PSG played well in the first half of the first leg without much contribution from Mbappe. They can do same without Mbappe in the second leg.
It seems Mbappe does not have good fitness with what I saw from his arrival in Manchester. If PSG scores first in the second leg, they will create panic for Manchester City.
You cannot judge PSG has no chance to win as long as they still have 11 players on the field. There will be another player to replace Idrissa Gueye, probably a midfielder who is more aggressive in attacking. Yep, I am pretty sure that PSG will make a strategy to be more aggressive in attacking and Mbappe must be there if he isn't injured. If Man City cannot defend solidly, PSG must have a chance to make 2 goals and defeat them. So, it is still not impossible to beat Man City as long as PSG still desires to qualify to the final stage.
PSG and Manchester City are strong teams and their players even substitutions can make differences. Manchester City will play at their home stadium but I am curious that how Pep will make his decisions for Manchester City squad in the second leg. In Champions League, any mistake by coach or players will be punished and sometimes such mistake will cause a serious defeat.
In direct big clash like this pair, and in semi final round, such mistake will be very serious. Pep is a coach who wants to make everything as perfect as possible and some failures of Manchester City in Champions League have contributions from Pep.
Manchester City will be able to secure the aggregated result and take a position in the final match if Pep won't make stupid perfection-obsessed decisions for Manchester City squad.