They sold a talent, but consider this, unlike last few years, where they had to sell key players regurarly every season for big sums, now they have gotten 50m from 2 players out on loan who they didnt want to use. So essentially, unlike before, they havent weakened their team at all, and just added to it. So they are in a position of strenghth more then usual, kept the unit, and got a big pay day from players that werent part of it.
Romagnoli sale is extra bad mainly because he is very young and their own youth product. But on quality alone, they should be able to find good CB to start with Castan eventually, I'm guessing next summer.