What would be the point of Childs abandoning his post at the end of the movie?
I'm confident that Childs isnt the Thing, but I also doubt his excuse of having seen Blair out in the storm.
The only thing I can think of is that he did something to sabotage the generator and left perhaps? The generator is just "gone" after all. It wasnt torn apart like the helicopter or the other vehicles. That kinda implies that a human did something to it as opposed to a Thing.
I also think that the Thing wasnt just scavenging for parts but also intentionally getting rid of ways for the humans to leave/call for help. I think that is why the Dog Thing sorta goes "mask off" and attempts to quickly kill all of the kennel dogs. The Thing is extremely smart and generally doesnt try to fight a fair 1v1. It wants to ambush it's target.
At the end of the movie I believe Childs moves from his post and ends up gaining an advantage against the Thing because of that. He is able to hide as the Thing kills the remaining crew and the station goes up in flames. He effectively puts the Thing in check. It cant hide anymore and it'd be far more difficult to attack the person out in the open. The Thing recognizes that Childs made an "illegal move" to put himself in a winning position like the chess computer in the beginning of the movie. Mac would have been pissed. The Thing is impressed, and yet it still manages to talk Childs out of his checkmate by convincing him that neither have the strength to kill one another, that they should just stay there and freeze to death. Childs accepts because he doesnt know if he is talking to Mac or the Thing and Mac seemingly was about to drink alcohol like he always does, then offers some to Childs. It's not really something that makes sense for the Thing to do. Why would it drink alcohol?
My alcohol theory ( https://old.reddit.com/r/thething/comments/1tewbiy/something_i_noticed_about_alcohol/?ref=share&ref_source=link ) keeps developing. In that post I say that it exonerates Mac from being the Thing because he's always drinking but perhaps all that really does is slow the infection rate and harms the Thing's ability to shapeshift. A Mac Thing would be very intelligent. It would understand the importance of sacrificing other Things in order to maintain it's cover.
The Things arent even allies necessarily. We've seen both in the movie and I think in the book at they're willing to kill each other or at the bare minimum help in destroying exposed Things. It's also likely that the Things might not even know who is and isnt a Thing as well. For example if Thing 1 creates Thing 2 and later on Thing 3, then the memories of Thing 1 might pass on to the new Things it creates, but that doesnt mean that Thing 2 would know Thing 3 exists. Where as Thing 3 has the memories of Thing 1 creating Thing 2, and Thing 1 has the experience of creating them both. This could lead to a scenario where Dog Thing infects Palmer early on, the kennel scene happens and part of the Dog Thing escapes, then it goes on later to ambush and turn Mac. This would give Mac Thing the knowledge it needs to throw Palmer Thing under the bus and regain control over the group of humans at a time where it is being highly suspected.
So why would a Mac Thing that just got done having to fight a Blair Thing that didnt know Mac was turned decide to pull out the bottle of alcohol at the end? Perhaps it's trying to build up an immunity so future Things it creates dont end up exposed or weakened like the Bennings Thing was? Or maybe it has so thoroughly imitated Mac by this point that it simply does it because drinking after a stressful situation is what Mac would do.