He should of got one more year if you ask me, mainly because of the poor transfer window but if he was given a decent window and got the same results then arguably you could say he should of gone. I don't think it's a case of this years trophy haul but rather the lack of progress that has lost him his job. After winning the title you'd expect to build on that and at the very least give it a very close challenge while progressing in other departments, that hasn't happened this year.
We finished this year 11 points behind United, out of the Champions league in the group stages having not even won a match and failed in both cups, one of them in an embarassing fashion. In hindsight, yes he should of gone but i still believe he should of got another year and a decent summer. You could argue that the transitional period to the new CEO and director of football is really what has cost Bobby because it's obvious in the summer we weren't wholly in the market of buying and improving the squad.
Now we have to hope Pellegrini will build on what Bobby has done and take us on to better things but at the moment things are a little worrying and the club needs to clean up this total utter mess.