Yep, it is a smart idea, but no guarantee to sign him in the next season. Except, Real Madrid has reached a personal agreement with Mbappe and also PSG management for the possibility of his transfer in the next season. I am sure Real Madrid management has considered everything to sign Mbappe, what I said before probably did by them.
Regarding the possibility of a player crisis this season, I don't think it really deserves to call a "crisis". Real Madrid still has many good players, especially in the attacking line, we should be so worried. There is Benzema, Bale, Hazard, Asensio, and Vinícius. Carlo Ancelotti just needs to optimize their performance with an effective strategy. The real problem is in the defense line, mate. They lose two key players, the strongest CB they have. I don't know if the current defenders are quite ideal to experience this season.