I don't know how Messi and Neymar would end up in this summer. But one thing is certain that Mbappe is everything for PSG right now. He is a much more valuable player than even Messi and Neymar combined for PSG in my opinion. Even their spending an insane deal of money on his contract should be an indicator of this for example. They are building their game over Mbappe in the end. Besides Mbappe can be one of the legends as well if he continues to play consistently for many more years.

It looks like PSG can keep Mbappe in the club at least for next season. Because it doesn't look like Mbappe has plans to leave in the near future. However I can't say the same for a season after. It might depend on how successful PSG will be next time as well. Because Mbappe wants to win the Champions League title with them. But if they disappoint people again then he might seriously consider Real Madrid's interest in him.