It's happened. It had to happen sometime, and so it has–Markus "Notch" Persson has stepped down as the lead developer of Minecraft. But there's nothing to worry about. The reason Notch is stepping down is that he's dedicating himself full time to work on something else at Mojang.
Taking over his position as lead developer of Minecraft is the equally talented Jens Bergernsten, whom according to Notch will have "the final say in all design decisions, so he will kinda sorta become my boss, I guess."
The two have been collaborating together on Minecraft for a year now, and Notch remarks upon how remarkably in synch the two are with the game's design. The results, as we can all see, are obviously good. Notch noted that he feels confident in Bergensten's leadership of Minecraft, so suffice it to say, the game's in good hands.
In the meantime, Notch says he'll be getting some much-needed rest after a hectic development schedule, and begin work on "some new project," which is as yet undisclosed. His other game Scrolls is still in the works at this point in time.
Notch says he won't leave Minecraft, and will continue to help with Minecraft's development.