If you look at the total cost, then I doubt that buying Mbappe would be profitable - it is unlikely that he will pay back the money invested in him. Haaland is much closer to that but it remains to be seen how he fares in terms of injuries - this season he has had a lot of missed games due to various injuries. If this continues then such instability will be a big problem for the club. In general, I think Real Madrid will find good alternatives. A whole summer ahead.
The thing about Mbappe is that, he may or may not recover the money spent on him, which is an uncertain thing, but it is clear that he will keep this team a great one for a very long time, that is a guaranteed thing for sure. I know that many people watch PSG because of Mbappe and their success. If they let him go, they would have to go out and buy another superstar and how many stars out there that they could buy?So, it is not so much about being profitable just from one player, but to keep the overall of the team higher with that player. I guess they will fail to build a great team around him from now on though, considering how much they are spending already.
Something similar was expected from Neymar
Do you remember how loud this name used to be? And now everyone absolutely doesn’t care about him and even like PSG wants to get rid of him (but they can’t haha because Neymar is satisfied with his cosmic salary for minimal effort). And I don’t know what kind of masochists are watching Ligue 1, even if only for the sake of Mbappe - in order for the league to be interesting, you need intrigue and several great clubs and not just one money bag that beats everyone.