Two Seveneves Speculations

In the novel Seveneves by Neal Stephenson, the Moon explodes, causing the surface of the Earth to become uninhabitable for 5000 years. The Pingers, one of the surviving groups, are descended from people who survived in submarines in deep ocean trenches.

In view of the fact that novels about the potential uninhabitability of the surface of the Earth, such as On the Beach by Nevil Shute have been around for decades, is it possible that various navies already have plans to do something similar? Let's see… It might make sense to have an all-female crew with a gallon of frozen sperm… They would need a hydroponics and a nuclear reactor…

Speaking of On the Beach, what would Rufus MacQuarie do in that situation?