A bit... Hmm. Conflicted. I can understand the decision. I don't fault Herr Persson for doing it, he's explained his reasons and they're all fair enough. He's been immensly lucky, and it'd be petty of me blaming him for taking the opportunity.
Not to mention, he could very well reinvest in other ventures further down the line, which would hopefully mean more job opportunities and more good games. I doubt he'll retreat to rest on his laurels for the rest of his life.
Even if he does, he's still paying taxes. Muahahaha...
On the other hand, I'm afraid for what Microsoft might do with the game. I'm personally in it for the mods. That is what interest me in the first hand. And I am worried Microsoft won't look too kindly to those and implement measures to stop them. While it wasn't particularly expensive, it'll be a purchase I won't have any further enjoyment from if vanilla Minecraft is locked down as the only allowed form of enjoying the game.
There will, no doubt, be something to fill the gap. Perhaps some Feed the Beast stand-alone, or perhaps EverQuest Landmark leads to something that'll scratch the same itch. Something will come along. But it'd be a shame if the potential of modded Minecraft was fumbled away by a detached Microsoft manager.