A good rule to follow is never to invest more than what you would be willing to lose.
Agreed, you need to invest only that much amount of money in any kind of investment which you can afford to lose because you never know whether you are going to end up losing or gaining more money. I dont really think so that there is any such reason because of which we can claim such kind of thing like that of disappearing of the bitcoin in the future. Bitcoin will remain there in this world and will keep on making us richer.