We should definitely try to keep him. Yes, it would not be the end of the world if he leaves, but, just look at the market. Many people here are betting on De ligt like he is already a proven WC defender, or like reports say Upamecano (who has 100M release clause, which seems foolish to trigger). These players are what you call, POTENTIAL SUPERSTARS. We have seen Umtiti's strengths, he has that talent, he has proven himself , he is well adept to the system, although he has been poor recently, its just a run of form, he has got that talent needed to succeed here, it is sure he will bounce back.
Why in the world people are hell bent on loosing a established player, over someone with a POTENTIAL to establish him here. Pique is 31, Verm is glass & 32 year old, Mina is clueless & inapt. The only mainstay CB we currently have is Umtiti (24, and a WC CB), why sacrifice him for a gamble like De Ligt or Upamecanyo.
I am not saying to give in to his demands, but rather find a middle ground, where both parties are happy. And After Roma game, people are just bashing him like he is a murderer. Yes, people's opinion may change, but if they change after every single game, its just childish.