At this point selling him for big cash won't be considered as a problem for the club IMO, they're unlikely to increase his wages significantly anyway. If he's on 8+4 at the moment, then how far is Juve willing to go for him? 15m or 18m net? I find it hard to believe when I hear these numbers. In this sense I see MDL as the new Pogba - the club will be forced to sell in the end.
IMO the real issue will be whom does Juve buy to relplace De Ligt and at the same time Chiellini/Bonucci. The club needs to find another Bastoni/Skriniar or at least Acerbi, someone reliable enough. Italy produces quality CBs all the time, it's just that we've missed out on all of them except for Romero and Demiral who are not here anymore.