for this situation, I think we can compare Zinadine Zidane and Ryan Giggs. When Zidane manage Real Madrid, in the first year he get a champions league with that players. And now with manchester united play in under champions league competition called Europa League, with their squad now they can win the europa league with Ryan Giggs.
Before taking the head coach position in Real Madrid, Zidane was a coach of Real Madrid Castilla and became coach assistant for Ancelotti in senior team. So comparing to Giggs, Zidane had more experience, thats why he got success in his first time as head coach for Real Madrid. But who knows, maybe Ryan Giggs could surprise us.
Well we know Arsenal is a big team but they dont win Premier League for years, and Arsene Wenger still there.
It totally depends on how patient the fans supporting their team.Not only the fans, but also the board of directors. If this is still about Man United and Mourinho then I guess their board members will not be that patient. But I can see Mourinho last three years at United before finally pulling the plug if there's no success seen by that time frame.
We know one board member who's really not happy with what's going on with his beloved club right now, Sir Alex Ferguson.