I absolutely believe that United is no longer for sale, but I do also think that:
A: This article is mostly based on guesswork.
B: The Glazers will never get a bigger offer for the club.
The reason for B is that we're very clearly on a downward trajectory as a club. Yes we have a manager that might do ok given his unfortunate circumstances, but we have terrible infrastructure, no investment and no knowledge of football within the ownership and higher up positions to fix the problems.
I've mentioned this before, but where I live, I had never seen a City shirt until a few years ago. Now they're everywhere, and it's becoming far less common to see United shirts. This is especially true with younger fans. I'll still see plenty of Liverpool, Arsenal even, but way less United ones. A while back I did some work in a local school and they had a sports-themed day where kids could wear sports kits or shirts. The amount of City shirts was shocking!
It's a matter of time before City are universally accepted as the bigger club. Fanbase is all we really have left other than history, and that's changing. The more years we spend looking foolish, being boring on the pitch and making ridiculous mistakes with the club, the more our value will naturally drop. Without new investment there's not really a way of changing this. The Glazers will come to regret not selling I reckon... Though I'm sure they'll rip enough money out of the club in the meantime to make them happy while we take Spurs rejects on loan because we're broke.