I guess it depends on how you define failure. If it's a young player leaving, maturing and then returning then I don't think they were really a failure to begin with.
If a player is at an age where they aren't a youngster and leave because they aren't good enough to get into the first team then it has to be done on a case by case basis and it depends on their role in the first team.
If United signed a player like Antony and brought in Depay as backup then, as long as he wasn't on mega money, I don't think anybody would be averse to that. However, he hasn't turned into a Salah or Haaland so shouldn't be leading the line.