I did consider your version but got confused by two things:
The sentence contains conditional clauses, which should normally be followed by commas ("If we didn't, we would be fired"). Is there a particular reason why the sentence doesn't need to be punctuated like regular conditional clauses?
Also, is the sentence a compound predicate (with the
Let me say that my second choice would be "He told us that, if we made it to the top of the mountain in one piece, we would be promoted and that, if we didn't, we would be fired." This treats the conditional clauses as parenthetical, which is what the single comma accomplishes when the clause is at the start of a sentence. I agree about the compound predicate, but I added the co