Unfortunately, it's a different world now. The established teams have manipulated football finances to the point where it's almost impossible for any of them to cease to be a big club. Even outside of the Champions League, the rags will still have a wage budget greater than anyone else in the league. Even if the Glazer's completely ruin the club, there will be countless investors lining up to take over. I could imagine an Arsenal or Liverpool-like period of not winning, but that's gonna be as good as it gets, I reckon.
I did enjoy Ferguson claiming that he'd left them with his strongest squad when he quit though, and Gary Neville claiming that he left Moyes with a squad that matched their 99 and 2008 squads, both claiming that the team is only going to get better. A few months later and now they're a team "in transition" despite having fewer changes than any other team.