Ferguson announced today that he will be coaching for at least 3 more years, if his health remains blossoming..
This will probably be the case.
And it means that his successor will be entering old trafford on the summer of 2015..
This is 3 more seasons and i bet my money that Mourinho is not going to stay - that long - to Madrid for various reasons, even if he manages to outclass barcelona untill then (which is not what will happen).
So two are the major likelihoods:
1) he joins city either this summer or the next one to replace mancini and automatically he loses the chance to coach united in his career.
2) - more likely to happen- he joins another team probably next summer, stays for two years and then lands in manchester to establish his 7-10 year reign in united..
What this team will be? it will be IMO a team of another league - not one of his past leagues England, Italy, Spain portugal - ..
Either Ligue1 or Bundesliga.. And most likely either pariSG or Bayern munich.. he will win for sure two legaue titles and maybe a CL those two years..