Interesting. I did see him as "transformed" from a mundane, pathetic Walt into someone who stumbled onto the thrill through an old circumstance which made it rational (dying, caring for family).. But you have a point.
I think Walt has been pathetic the entire time. He tries to become this Heisenberg character, and it's just that, a character, a form of acting complete with costume change. It's a facade he puts on to appear tougher and more in-control than he really is. Walt's basically been winging it all along and has become more destructive to himself and others over time.
Jesse leaving was hurtful to Walt's pride, his sense of routine, and his whole "empire" build-up, but as we saw this ep, he tried to overcome that very quickly, almost reflexively. He simply used another young guy as someone to mentor over and to act as basically a surrogate Jesse, and continued forward. He doesn't tend to let things stop him for long.
When it comes to Mike's death, Walt will do what he eventually always does when he's the cause of some unfortunate act: he'll rationalize it and move on. With the events surrounding Jesse, Mike, and everyone and everything else, Walt views them as temporary stumbling blocks, and his defense mechanism continuously pops in to fix the problem and he moves on. And now you're starting to see him truly crack as all of the pressure from that builds up; the fidgety, hesitant Walt you saw shoot Mike shows he's starting to crumble to some extent, and that he won't be able to keep the masquerade up for much longer.
Walt can't allow anything to stop his forward momentum in any way because he'll then actually have to consider all of the actions he's taken in the series. The guy went off the rails a long time ago and that train is about to crash hard.