I think the ability to work on what you feel like and creative exploration is fine, but when there's a considerable gap between your last qualified success (or a lengthy period since you last actually completed something you were interested in), it should be a warning sign that you need to knuckle down a little.
Success is a thing in of itself, it doesn't require repetition for validation. If notch is in a place where he never needs to meet your criteria of success ever again I'm sure he would be quite happy.
One second thoughts, having been on the sidelines of gaming communities for a number of years, I imagine that not having to feel like you need a success ever again is probably the best possible outcome as an indie game dev.
Also some of the Ludum Dare stuff he makes is pretty amazing. And he is giving a huge boost to WebGL now.
Looks to me like he has continued to code awesome stuff. Just because something doesn't suddenly earn millions of dollars doesn't mean it isn't a success.
Life isn't all about money (which he already has a lot of) and pumping out products.