The only way Man Utd would get relegated is if there were some financial/bribing a ref type scandal as there was in Italy a few Years ago.
Chances - slim to anorexic.
With 10 points covering all the teams in the Prem from 7th (Wigan) to bottom (West Brom), any team in that section COULD go down, including Man City; realistically however, given their potential to buy whomsoever they want in Jan, I can't see Man City going down in May.
If, for sake of argument, they WERE to get relegated however, the only thing you can guarantee is that their home gates would still remain mid 30K; whether or not their Arab owners would want to stick with it is another matter however!