1. Then, could I be understood that past perfect - such as 'had come/bitten' of in a conditional is never simplified into simple past?
The only case I can think of where the past perfect could be simplified into past simple in an if-clause could occur when both express real past, for example:
- If you said a vampire had bitten you, how come you have no marks on your neck?
- If you said a vampire bit you, how come you have no marks on your neck?
2. When you view 'came/bit' as real past and 'would have been' as hypothetical future from a past perspective, the whole sentence is a mixed one with an indicative mood in the if clause and a conditional one in the main clause?