Being a Buddhist isn't as simple as it appears. The idea is to reach a state of Nirvana by renouncing anything sentient in human life. I'd guess the goal of self-mummification is keep one on the path rather than to become a worshiped god. Buddhists don't believe in a creator or supreme being after all. They just want to get out of their bodies and become at one with the universe. It's just a bonus if you end up being deified.
A mummified body's been dug up (again) recently. The Buddhist who self mummified's said NOT to be dead, but in a deep trance! Followers believe that the mummified Mongolian monk's simply about to reach enlightenment ... even though he's been in his present state for about 200 years. : )