The Gnostics were hunted down and killed while others had to go into hiding..
They still felt that this type of knowledge was worth dying for so they went underground with they're work, however the nag hammadi chronicles are far from complete. There were parts and even whole gospels that were omitted or not found (perhaps someone can get into the vatican and retrieve where some of them may be) Thankfully though what we have remaining (the things that were excluded from the Bible) is enough to gain gnosis (esoteric knowledge of spiritual truth held by the ancient gnostics essential to salvation and knowledge from the heart) Once one has Knowledge and Wisdom they live in pure spirit and are in the world but not of it.

How one persons gains they're gnosis in a lifetime will be different from another persons. Just to be very clear on some things, gnosticism is not a religion. Its a way of life/living and there are no prayers, mantras, invocations or worship needed. Gnostics aren't priest and don't belong to a priesthood class. They are merely messengers of a divine message from Sophia and Christ!