Played with your prompt a bit, since sad apocolypses aren't my cup of tea. I don't know if there are happy apocolypses, but um, I went for a happier...thing. Yeah, sense, I make it.

Also, I cheated and made it four sentences, because I couldn't get it all done in three. I am a rebel!

Written from an iPad forgive any autocorrect zaniness.

John supposed it wasn't surprising that Sherlock insisted on closing the case, even after John made a -- he thought -- excellent argument for how it wasn't going to bloody well matter in twenty-four hours, you complete nutter.

John supposed it wasn't surprising that he'd chosen to stay and help Sherlock close the case, rather than run for safety like any sane person would have done -- he was too much a soldier to leave a man behind, especially his best friend, no matter how insane that friend was.

John supposed it wasn't surprising that they were literally the last two people on Earth at the moment, and that Sherlock was completely unconcerned about it, or under any sort of impression that the ships that were leaving the planet wouldn't wait for him to arrive.

He supposed the only real surprising thing was that the ships had waited and the case had been solved and now John was going to have to put up with a smug Sherlock for thousands and thousands of light years -- and that it was all really quite fine with him.