"Those of you objecting to the behaviour of the charactars as carrying on as 'normal' - what would you envision them doing instead?"
I sincerely recommend that you read a couple of books in the apocalyptic/post-apocalyptic genre if you are really asking this. Or watch some movies like Deep Impact, Armageddon, War Of The Worlds, or 2012.
What those people should have done (and would have done, considering normal human drive for survival) is to never stop looking for a way out of their impending doom - use that submarine of theirs to transport everyone further South, dig living spaces & corridors and fashion home-made air-filter systems to live underground for as long as they can, hoping the fallout clears in a year or two. Stock vitamins, medicine, antibiotics, long-lasting food in cars and tins. Fight each other for a space on that submarine as it goes towards Antarctica, where their families can at least live several months longer.
Whatever, really. ANYTHING but sitting around like morons, talking about whether they should wait for hunting season & who will next get married and have babies, knowing full well that they will all be dead in several months.
"I think it's psychologically convincing that people would deal with the end of the world by pretending it wasn't happening"
ALL of them? A man saying he should take a job in another city and leave his wife and baby to die without him because it is good for his career - even if he is delusional, wouldn't you clobber him with a stick if that was your husband abandoning you while death approaches?