Nobody would have. Because it's not possible to win everything all of the time. Nobody can do that.
Ferguson and Wenger have only survived this long because they have a good board behind them. They know that these managers can bring success and results. They have faith in the manager.
I feel sorry for Carlo Ancelotti and Mourinho when he was there (or even Avram Grant). They did the best they could, but there's too much interference back stage. It's a farce. The manager doesn't control the team, Abramovich does.
Anybody who takes that job is either really brave, really needs the money, or is really foolish. They made a massive mistake in getting rid of Carlo anyway. He's a decent bloke.