Mbappe must be in Madrid first eleven. Garcia had the opportunity to play because Mbappe was sick. Mbappe is a goal machine and has more experience than Garcia. There is time for everyone to play in Madrid and that's why Madrid is keeping these young players. Mbappe was the highest goal scorer last season so don't underestimate him for a lad.
Even Gracia at some point will understand that it was a privilege he has been playing all this while due to Mbappe's situation, as soon as Mbappe returns, he is not going to be kept behind for Graci, not after all the team spent on him and so far they have seen his exceptionality and potential, Real Madrid is adding him to their first eleven squad and that is not even in doubt. Last season Mbappe did so brilliantly I do not think they will want to risk keeping him when he is in his good form knowing what he is capable of, xabi Alonso will bring in Graci at some point because he is a very good player also.