There is a lot of time left until the end of the summer transfer window and this is in Endrik's favor. He can recover and have time to pass the medical examination for a transfer/lease. I think he has no chance of getting into the main team next season, he should now choose the option where he will play in the starting lineup and get real experience.
The problem is that he can play as a striker only. CF or SS. Only if he starts adapting to playing for example as a winger then he might have more playing time.
Otherwise yeah, it is unrealistic for Endrick to cut Mbappe from the starting lineup of course.
Better to loan him then.It's a problem to get a place in Real's starting lineup, but overall there seems to be a shortage of players in these positions on the market. Naturally highly qualified. Endrik needs to leave and prove his right to be at Real Madrid in another club. It seems now, if he is really worthy, he will be able to push aside the old guys who occupy the first positions in the scoring races. In an average or near-top club it is very likely to do so, but not in Real at the moment.