Is "where" suitable here?

In your sentence, "where" doesn't quite fit because it's more commonly used to refer to locations. A more natural alternative would be: * "I don't care whose parts are frozen *where*!" could be changed to: * "I don't care whose parts are frozen *to what* extent!" or * "I don't care whose parts are frozen *in what condition*!" This way, it keeps the meaning of something being frozen to a certain degree or state, rather than a physical location.

No suitable. The use of "to death" is hyperbole and metaphor for a state or condition, while your use of "where" is for physical location, so there's a mis-match. Instead: \- Our hands are frozen to death! \- I don't care how badly frozen they are!

I think this kind of wordplay modifying an idiom can be pretty flexible, I can imagine myself saying "to where" here or finding someone else saying it clever. Others seem to disagree

It could work if you’re trying to make a joke, because this isn’t the expected use of the word “where”. “To” in this context denotes extent, not location.

'To what' would retain some of the wordplay. If it were 'burnt to hell' or something similar, 'where' would make sense.

It depends. It wouldn't work if the literal intent was sincere because "where" is indicating a location, and "death" is a state of being, not a place. With that being said, this would work if it's intentional. It would be a very logical and normal type of wordplay where one type of word (a concept/condition) is intentionally and absurdly misinterpreted as another type of word which would also be grammatically appropriate in its place (a location). It could be done purely for humor or as a subtle dismissal of the exaggeration that their hands are freezing "to death".

I doubt most speakers of the Queen’s English would approve. Americans will accept it. There are a few technical things wrong but who cares? It would come across as humorously and intentionally incorrect in most American dialects. Culturally, we’ve all agreed to ignore those inconsistencies so long as it works and it has flavor. And it does. I can see a native speaker saying that in conversation.