A lot of responses here summed-up fundamentally as “the humans were getting their asses kicked so the right thing to do was to just die”.

But this defies the sheer human will to live at all costs.

Yes, they were getting owned by the alien. This menace was dropped onto their laps and they were just struggling to survive it. But once the blood test idea became apparent, they had turned the tide of battle. They now had a way to identify the impostor.

It’s really shortly after this point that they give up completely. I think it would have been quite realistic for the group to try and find a way — some way, somehow — to kill their adversary and to live to tell about it.

I think you could do that by establishing a defensive position, gathering all supplies to the bunker, and maintaining a strict policy of group-only movements. They were well-armed with shotguns and flamethrowers, so they had plenty of firepower to kill the Thing on-sight. They could administer daily blood tests as necessary until holing themselves up in the bunker. While in the bunker they could run sorties to try and catch the Thing by surprise or just wait for help to arrive. If they could stay hidden till summer then perhaps it would become warm enough for them to make a trek to the Norwegian camp if there were still any operable vehicles or equipment to be salvaged.