He should have started the armbar escape in mid air as well.
That's also how Roger escaped in his first match against Buchecha.
Looked like he did a pretty good job of staying a little on his side to keep that shoulder elevated. It buys time like the way Vinny Magalhaes survived against Werdum and held out until the clock was up.
Another thing he could've tried was pushing MM's left leg up enough to get his own shin behind MM's knee. If you can drive that leg away you can usually get out.
It was a great submission though. There's no saying, if he did X he would've gotten out. Just a few other possibly/maybe type things.