He was dying and gave up. Probably realized he didn't have the energy to survive anyway and there's no way it's a guarantee he kills Walt in that situation when his gun is already drawn.
The way I see it Mike at that point gave up, he wasn't really running anywhere, **** was a wrap when Hank found out about the account in his granddaughter's name which was seized for the most part. He given up and probably reflected on all the times he ****** up recently and all the times he's ****** up since he met Walt. He should've killed Walt, he should've killed Lydia, probably should've killed Jesse when Gus said to but hey he went against his gut instinct and this is where he ended up, almost out the game but not in enough time.
I don't really see this season as rushed or much cramming of a lot of things in one ep, nor do I see the convenience in this ep, especially with that last scene.