What you will do if that thing will happen someday??
This is an impossible thing and it will not happened but I case what you are saying is right then I and most of my friends here on this forum will be in deep deep trouble as we all lose huge amount of money.
Not only your friends but all people who do engage on crypto world will surely lose money specially on those investors who put big amounts of money to invest on these field.Disappearing all coins would really be impossible as long there are people who do support it this thing wont really happen at all.Unless if theres a great EMP would hit on earth and do shutdown all electricity which would really bring a chaos for sure but thinking off its an impossible thing to happen.