tip: lex m/m (mature OR explicit)
I almost didn't read this, because I generally don't do well with apocalypses, and also because I read "The Last Policeman", and the creeping horror of imminent and unavoidable ending sank into my *bones*. But you've done something very marvelous here, in that Holmes and Watson together are still so very themselves (the voices are perfect)--are what Terry Pratchett calls "a tiny 'yes' in the night", even such an oncoming night as as asteroid might cause. There is no hope in "The Last Policeman", but you've written hope here, and whether the two of them (plus Ms. Hudson and Alfonso and Clyde) ride out the aftermath in Argentina and continue to thwart Moriarty, or whether they do not let go of each other as darkness falls, they will still be doing what they do best, solving crimes and being each others' anchors.
I actually haven't read "The Last Policeman" for exactly that reason! But I am glad you liked the thread of hope here, and the character voices. And I love that bit about the "tiny 'yes' in the night." Thanks for this beautiful FB!