What Julian should have done is sued Mojang in the first place. He didn't defend his "copyright" that he claims to have when he should have. So in court, he probably would not have won - even if Microsoft would have dragged this out for an extended period of time and exhausted financial avenues.
IANAL!
The statue of limitation on copyright infringement is 3 years, as far as I am aware. So while Julian does retain copyright, he cannot sue Mojang for copyright infringement. When Microsoft bought Mojang - the infringing party is still Mojang - the company still exists, and the game is still being published under Mojang.
He is more than likely aware of this, and hoping other people aren't. He's trying to spin this as the little guy vs Microsoft, but that glosses over the detail about the statute of limitation on copyright infringement.
He was hoping to shame Microsoft into settling, but legally (and ethically, I would say) Microsoft doesn't have to. So he puts it into the public domain. He thinks he's played the smart hand, but now Microsoft is legally allowed to subsume Mojang without worrying about triggering a fresh round of copyright infringement.
The 1700 lawyer legal team probably wisely counseled Microsoft in staying quiet. Lest they speak and appear the fool.