The problem Man Utd have (and Ashworth had) is that they need to overhaul their squad to play a 3-4-3.
If Amorim does not work out, they've then got a squad wedded to that formation so his replacement needs to play that way too.
If this works for them (and tbh i think it will), they're golden, if it doesn't, they'll be even more fucked than they are now imo.