PSG team management could not collect anything great from a player like Lionel Messi. In fact, I think the PSC team coach does not know how to play Lionel Messi. However, if Kylian Mbappe ever leaves PSG, the team will collapse.
In general, PSG has never depended on just two players and if PSG did depend on just two players, it was clear that the team would collapse because the team did not respect the other players in the team. But for next season what PSG really needs is a great young player even if he's not a star, because the PSG team can't keep hoping for one or two star players who aren't young anymore. So PSG must be able to find great young players in the transfer market before next season starts.