If a man has oral sex with a female that has bv but didn't kno it, can that bacteria survive in his mouth. can he reinfect her if his mouth has the bv?

Probably not: Bv is an overgrowth of lactobacillus that lives in the vagina normally. It causes a discharge with odor (but no itching). It is unlikely that the ph difference in the man's mouth along with the saliva would allow the bacteria to survive, much less be transferred back. The gal can be treated with either a vaginal cream or oral medication, and that should solve the problem.