If they were going to have him, he should have gone after Ferguson retired. However they decided that there was still such a thing as the Manchester United way and ended up with Moyes, Mourinho isn't a long term appointment.
They trail other elite clubs in their medical infrastructure so badly that some of their players prefer to use the specialsists employed by their national teams, the academy is miles behind Man Citys. No elite players would choose them, Sanchez only went there after they threw silly money at him, ditto Pogba.
I would imagine they'll go for Poch or Zidane but I can't imagine either wanting to touch it with a bargepole.