In forming negative sentences, "don't" is used along with the main verb (except to infinitive or modal verbs). As the context refers to an action that will occur due to some other not happening, the sentence will become a negative sentence and take the negative auxiliary "don't" which is the contraction of "does not". This indicates the action 'do'.
Thus, option C is the correct answer.
"Isn't" in option A is incorrect as it indicates the auxiliary 'be'. Here, the reference is to an action actually happening, so the verb 'do' should be used in its negative from.
"Weren't" in option B is incorrect as it is the second person singular past, plural past, and past subjunctive of the auxiliary verb "be". Here, the reference is to the actual action , so the action verb 'do' should be used.
"Wasn't" in option D is also incorrect due to being the past tense of 'be'.
Thus, option C is correct.