Forcing people to believe in cryptocurrency is not necessary. People themselves must be interested in the advantages and opportunities provided by the cryptocurrency. Regarding the duration of the existence of cryptocurrency, here while we can not say anything definite. Cryptocurrency is still about ten years old and its development encounters strong opposition from states that do not benefit from the existence of cryptocurrency, since they cannot control the cash flow in the cryptocurrency.
So far we can only say that nothing is eternal. Everything eventually disappears or is transformed into other, more perfect forms. About the duration of the existence of cryptocurrency can talk in 50 - 100 years.