Ramos definitely looked like a great player, I think it wouldn't be really that bad to just not even buy any new players and just play the same PSG team without Mbappe, they would still win the league with this squad if you ask me. But, they won't do that because they have money, and when you have money that means we are not going to end up seeing someone who will do further, we are not talking about anything more.
If they do not make any adjustment to the team by introducing some new signings outside of the French League following the exit of Mbappe, trust me if I tell you that their highest achievement will be the French Lig 1 title next season. They should never nurse any ambition of getting close to the semi finals of the champions league like they did this last season. I am not saying that they do not have good players, just that the squad is not just competitive enough to face other tough European teams like Bayern Munic, Man City or Real Madrid. You should not forget that it is expected that Mbappe leaving will create a huge vacuum in the team which require an external person to fill.