In this post (Using just Past Simple in the Third conditional) Michael Swan says:
262 if (7): other structures found in spoken English
4 mixed tenses
Sometimes a simple past tense is used with if where a past perfect would be normal. This is more common in American English.
If I knew you were coming I'd have baked a cake.
If I had the money with me I would have bought you one.
If I didn't have my walking boots on I think I would have really hurt my foot.
However, Swan does not give examples for the verb to be case. I wonder if American speakers -informally- also use the past simple for verb to be too in counterfactual (unreal) past situations.
It seems that this thought is possible in theory. There is this quote for an Australian speaker on Yahoo News
It's likely a police officer who was shot at a Sydney hospital would have died if he wasn't in the emergency ward at the time.