Past perfect usage in hypothetical statement

Question

On Quora, I've run into such a sentence where the author describes a hypothetical situation if astronauts wore unsuitable space suits on the Moon:

At about this time, they’d realize that the sides of their body in shadow up till now had grown very cold and those in the sunlight were uncomfortably hot.

I don't understand sequence of tenses here. Does a sentence describing a hypothetical future situation requires past perfect in constructions like this?

Which is correct?

If this occurred, somebody would realize something had happened.

If this occurred, somebody would realize something has happened.

Is past perfect used because the whole clause is shifted to the past in conditional? And what if we are talking about hypothetical past? Do we just add have after would? For example:

If this had occurred, somebody would have realized something had happened.

Answer 1

they’d realize that the sides of their body in shadow up till now had grown very cold and those in the sunlight were uncomfortably hot.

If you tranform this sentence into the real situation, you will have

they realize (are realizing )that the sides of their body in shadow up till now(by the present moment) have grown very cold and those in the sunlight are uncomfortably hot.

Since the situation is hypothetical you use would instead of will and that requires backshifting into the past.

I don't quite see the connection between the first and the second parts of your question, but the first and the last sentences are grammatical,though you can do without had in the first sentence.The second sentence is ungrammatical, because there's no sequence of tenses(has).