“Would he have a chance of remarrying a girl that never married before or are they [sic] ‘doomed’ to be single forever?”
First of all, there’s always a chance. Second of all, he can also marry a widow. My mother is a widow, and often gets matched up with Kohanim.
I do know one very happily married couple that is the opposite way. He is a widower (not a Kohen, as far as I know) and she was never married. His kids were already grown when they got married and she was unable to bear children. They are seeking to adopt. I think they’ve been on adoption lists ever since they got married a few years ago, but newborn babies are in such high demand and especially for them as an older couple, they aren’t an adoption agency’s first choice. I know they have been through a lot of tzoris dealing with the agencies. But I don’t think that their different life experiences presented an obstacle for their relationship. They seem to be very happy together.