I think you are ignoring the condition on that sentence.

"Once sales start dying and a minimum time has passed, I will release the game source code as some kind of open source."

Sales will, at some point, start dying. He has, as far as I can tell, relinquished control of the source in a manner that will forbid him from open sourcing the game at that point.

You think it's reasonable that he should continue at the helm of Mojang and retain control of Minecraft IP until what exactly? 10 years pass and the brand (which Minecraft has become) finally fades in popularity?

So he can release it as open source, to make good on what? Some "About" page he wrote fucking 4 years ago when Minecraft was nothing but a PC indie sleeper hit?

Get real.

So what? He should screw his business partners out of 2 billion so he could keep a promise from years ago when he had no clue how this would go?

Especially a promise to a community that throws him under the bus whenever something happens they don't like (even if he isn't involved)?

I don't think that is reasonable.

I agree. That's why I don't recommend ever open-sourcing any software with commercial possibilities. You'd be throwing money away.

Right. He never thought he was going to make the current juggernaut. He thought it was going to be yet another moderately popular project with a limited duration and impact.

He didn't really.

"Once sales start dying...as some kind of open source".