In the first theory, Mbappe is a great player losing this player can damage the team in PSG as you said and this would be so hard for this team to find a replacement for Mbappe in PSG there is no team they want to lose a player in the level of Mbappe easily and I think PSG can't find alternative players in this team among younger players if they lose Mbappe.
But on the other hand, we can't forget what happened in Tottenham when they let Harry Kane leave the team, this team was not damaged but they even got stronger than before.
I think so too, especially now that PSG is exaggerating Mbappe's presence so much that other players are covered up even though basically a team's performance depends on the performance of all players in all lines, not just one player.
As an individual, Mbappe is quite great and I think for now he is one of the best players in the world, but for PSG I believe they would be better off losing Mbappe so they can build this team with a strong foundation and also all lines with the same quality of players so that it can lift team performance as happened to the Tottenham team.
You are right, individually Mbappe is a great player, but in football what is needed is team play and not just focusing on one player. Indeed, the presence of an above-average player would be an advantage for a club, but it should not lose sight of what it should be, which is team play. When they still have 3 star players they still can't do anything at the European level, it proves the presence of star players does not guarantee success for a club.
They can still be a giant club without star players, with a note that they must have evenly distributed players on each line who can work together with good chemistry. I personally if faced with 2 choices between having their squad with good team play and a squad that has several star players, I would prefer to have an evenly distributed squad that can play good cooperation.
The team does not need many star players in the squad for a good performance. We have seen proof of this several times. The Chelsea team won the Champions League title a few years ago. They did not have many star players in their squad. Leverkusen are still unbeaten in the Bundesliga and Europa League this season. This team also has no star players in its squad.
PSG had many star players in their squad, but their coach was not good. There was no friendly relationship between the players in the squad. PSG team cannot do well in Champions League due to lack of friendly relationship between players and lack of understanding between players. But now PSG has an experienced coach like Luis Enrique. Now, if PSG's squad was as strong in attack as before, PSG would have been able to dominate the Champions League.