No one is obligated to make themselves miserable by forcing themselves to assume a role in life that they do not want. It might be debatable if he was some sort of political leader or humanitarian icon or something, of the sort where humanity's misery index actually increases in their absence.
However, for all of his good qualities, like 99.9999% of humanity, Notch is not wired up to be a hugely public figure, who is constantly interacting with the public, and is under continuous scrutiny to make another Minecraft. That's right, for the rest of his career, everything he does will be held up to the yardstick of being "the guy who created Minecraft".
I know, boo hoo and all that, given that he is now possibly a billionaire (on paper at least, and maybe only before taxes, but still!). But that doesn't instantly change his psychology- it doesn't flip any of the axes of whatever his Meyers/Briggs personality type is. If he's not comfortable and not happy being a public figure that everyone stares at waiting for the next Minecraft to pop out, no one should be able to hold that against him. He's not obligated to continue being that guy if it's not who he is.
After a few years out of the limelight, if he wanted to he could be a Mark Shuttleworth kind of guy: someone who struck it big while still young, and decided to invest a chunk of that money (and most or all of his time) to a passion project. I've gotta think that after the Microsoft deal, Notch won't have to work, but maybe in a few years he might decide to reinvolve himself with the community in a role that is a better fit for him. Or not, it's up to him. I would personally like to see some kind of Act 2 from him, because he is clearly a very creative and occasionally inspired person, but I won't hold it against him if doesn't want to.