We're probably losing Pogba this summer.
Odds are good that DDG will want away as well, and while that doesn't currently look like a big loss, it still means that we'll have to break in a new keeper. That's always a bit of an ordeal. Keepers are very often poor in their first season.
While Bruno hasn't shown any signs of wanting away, I can imagine he'll start to get offers if he continues the incredible start he has had here. If we don't start to seriously compete for trophies, I expect those offers will begin to look tempting.
Rashford and especially Martial increasingly look like they're not the strikers we had hoped for, and we'll need to look for a natural goalscorer who isn't 34. These two will not become our Cole and Yorke, that seems clear by now.
Whoever takes over from Ole, he'll have on his hands what is essentially a rebuilding project. And that's after we've supposedly been rebuilding for seven years. We've got a young squad, but the trouble with young players is you never really know if they turn into anything. How many have we had who looked highly promising around 20, only to leave for a mid-table team a few years later when it turns out that they hit a ceiling that proved too low? I have a strong suspicion that this will be the case for several of the players that many currently regard as the future of the team.