To be fair, he'd always planned this to be temporary. In his podcast with Tim Ferris just a couple of weeks ago, he said he'd be stepping down pretty soon.
But he is leaving at the worst possible time. A big upgrade requires months of follow up work and he should know that.
I'm not usually an internet tough guy, but this is outrageous. If I was a digg engineer I would be livid. The captain sailed into uncharted waters and then abandoned ship. He should protect his crew. He should do everything in his power to save the ship.
There's been a steady stream of digg engineers (and product managers, dbas, sysadmins, VPs) heading out the door for at least 2 years. So the ship is long since abandoned, the "captain" stayed on.