Theory:

If...not means the same as unless. Unless is used instead of if...not in conditional sentences of all types. The order of the clauses doesn't matter with sentences using unless.
Unless + Present Tense
Example:
1. Children will be sick if they don't stop eating junk food.
    Children will be sick unless they stop eating junk food.

2. I won't pay if you don't deliver the provisions immediately. 
    I won't pay unless you deliver the provisions immediately.
Unless + Past Tense
Example:
1. Rahul wouldn't eat that pork if he weren't really hungry.
    Rahul wouldn't eat that pork unless he were really hungry.

2. Sukeerthi would be here by now if she wasn't stuck in traffic. 
    Sukeerthi would be here by now unless she was stuck in traffic.
Unless + Past Perfect
Example:
1. Our boss would not have signed the MOU if he hadn't had an auditor present.
    Our boss would not have signed the MOU unless he had had an auditor present.

2. They would have killed Claudia if she hadn't given them the handbag. 
    They would have killed Claudia unless she'd given them the handbag.