My nieces mom got pregnant after her tubes were tired and a friend got pregnant after her guy had been fixed for a few years but never heard of pregnancy if both were but anything is possible I suppose
Did he ever go to his follow up to make sure his count was at 0? It doesn't matter how high it was previously - a vasectomy clips and cauterizes the vas that the sperm travel in. Sperm are still produced, they just can't get out. If he didn't go back, it's possible that it wasn't done properly and he has some left. However the odds that yours AND his would fail are astronomically low. There are dozens of reasons to miss a period outside of pregnancy, even if it's not normal for you.