My daughter was in the posterior position. I did end up having a c-section but I don't think that the position was necessarily the reason as I also had a c-section with my son. For some reason, I just didn't dialate. Anyway, after being very scared of having a c-section, I found that the worry was unfounded.
At the end of the day whether you deliver vaginally or via a c-section, you'll have a beautiful baby to love.
Good luck!