What happens to Pai and Yakumo in the manga storyline after the point where the anime ends?
There are many, many more volumes of 3×3 Eyes manga that have yet to be animated. Obviously, a lot happens, and it cannot be explained briefly. There are some manga translations and synopses available online, and if you are really curious your best option is to buy the manga yourself. If you have a specific question, ask on the 3×3 Eyes Mailing List (see below) and someone there will probably know the answer.