Your concerns are well grounded however. Bitcoin may indeed evaporate tomorrow without leaving a trace. It is written (or used to be, haven't checked the domain for a while) on the bitcoin.org website. It is experimental tech which nobody knows how it is going to end up.
Just because stocks went up higher during the last decade you don't invest 100% into stocks. You diversify.
1. Bitcoin is not experimental. It has been around 13 years, it runs on open source code which means that anyone can check the code and verify how it operates. Every single line of code. So there is zero question marks about how it operates and on what rules it operates. Also, it does not operate on any website. It operates on those thousands of machines that keep up the one and only Bitcoin blockchain.
2.1. Bitcoin could evaporate? No. Bitcoin runs on thousands of miners and nodes around the world. To be able to disappear, all these machines would need to be destroyed and people running them to be killed. Or else we can just run it on new machines. So this evaporating is kind of impposible to achieve.
2.2 If you mean by evaporating that it's price could go to zero tomorrow, again you need to think more about what would need to happen for that to become reality. Bitcoins price comes from supply and demand. And as long as there is demand (buyers) the price cannot go to zero. So price to go to zero there would need to be suddenly ZERO people in the whole planet who wants to buy Bitcoin. How would that happen? Only way would be if something better money gets invented and we have nothing better in the world at the moment. And even if we invent something better in lets say 200 years, it would be slow transition taking years from older monetary system to the new one. Just like it takes years now to move from fiat standard to Bitcoin standard.