To be honest he did the job he that was given. Got rid of the deadwood, rebuild the team and transitioned to possession football. The tasks for this season was CL football and a trophy, he missed the former by goal difference and won the latter. Certainly a disappointment in the end, but hardly a collosal fuckup people are making it out to be.
It's easy to wank about his spending, but people forget what kind of monumental rebuild job he had on his hands. The squad that he inherited had a total of two players that weren't ****, Mata and De Gea. Now you have the best backline in the league, much improved midfield, and some of the most exciting youngsters in the world of football. Not too shabby for 2 years of work.
We can only speculate, but pretty sure he would never get fired if Mourinho wasn't available. For all Jose's faults, you can't pass up an opportunity like that.