@shishiristi, My Tibetan teachers, I practice Chod and Dzogchen told me that Bon was/is a separate religion but incorporated many of Buddha's teachings and principles. I was told Bon is a mix of indigenous religions and beliefs of Tibet and Buddhism. However, scholars and archeologist have different arguments.
Bon was the pre-Buddhist religion of Tibet, its central figure a king with sacred powers;
Bon was a form of Buddhism that developed in western Tibet at least as early as the period in which Buddhism was introduced into Tibet, and was similar in many respects to orthodox Buddhism;
Bon, so-called, was not a religion in its own right, but the sum of all the indigenous beliefs, cults of local gods, popular rites, etc., that were once prevalent across Tibet.

I don't have a bone in the arguments, but how religions form and dissolve is interesting to me!