In the sentence
"If it hadn't been for the accident, he would be alive right now"
we are using mixed tenses since that's what the context entails. The cause was in the past but the result is presenting itself right now. Now, given that the cause happened in the past, would it be wrong to say
"If it weren't for the accident, he would be alive right now"?
Can we always use them interchangeably when the result clause is in the present?