Most sources state that the teacher in 1872 attained a level of realization known as rainbow body.
According to one source, he deliberately did not, but reduced his dead body in size and transformed it so that it would not decompose. According to the source the small body is now hidden at a secret location.
Chögyal Namkhai Norbu Dream Yoga And The Practice Of Natural Light. Edited and introduced by Michael Katz, Snow Lion Publications, Ithaca, NY, ISBN1-55939-007-7, p. 89.