So whether Sancho leaving was the better choice or not will always remain to be unknown, but I'd say he's done more than well enough for himself since going.
Unfortunately, as the post above suggests, it was more the reaction that was the issue. Because Sancho left, every young prospect should leave. Ignoring the countless that did and never quite hit the heights.
Truth is, whether Sancho left or not, and also whether Foden stayed or not, they both would have turned out great. These are two young players with far higher ceilings than most. The only thing that could've held them back is a manager like Solskjaer.
I do feel though that this is probably the 1000th time now that people should realise that having a bit of patience and trust with Pep over a player can go a long way.