This question can be simply answered by pointing to direct selling companies operating at the moment, mentioning when they were established: Southwestern (1855), J.R.Watkins (1868), Vorwerk(1883), Avon (1886), Kleeneze (1923), Tupperware (1946), Shaklee(1956), Amway (1959), Mary Kay (1963), Oriflame (1967) and Natura (1969).
Considering how long these direct selling companies have been operating using the network marketing business model, clearly this is a long-term business.