I think even if the bitcoin decreased by the years passed it wont still be actually disapperad forever because some of the people store their bitcoin on a safer wallets(hardware wallet). If the volume of the bitcoin decrease the value of it may pump or get a higher value. and the chance that the value increase some of the people who store it may sell it on the market to get a big profit for it .
I agree, and I also don't think Bitcoin will disappear but maybe it's value in time will increase but I highly doubt it will disappear. It had contributed and helped a lot of people, for sure those who are holding on to their bitcoins for a couple of years would agree because they are most likely holding on to bitcoins because they are all hoping its value will increase in time more than what its current price is at.
Following the logic that nothing is consistent in the world, another type of cryptocurrency would surely take its spot at the top. The problem with bitcoin is its slow transactions and many prohibitions by countries in the world. Maybe in the future, there will be a cryptocurrency that is better, faster, and reliable than bitcoin but it will remain as a foundation to all cryptocurrencies.
People are becoming more wiser in terms of securing the bitcoin due to the fact that so many other holders of bitcoin have lost they assets in the past, and at this moment people have learn to spread the bitcoin in different places and even if they lost some part of it they will still have other saving to fall back to. So bitcon can not go out of existence.
People would just hoard and circulate their bitcoins until its value skyrockets. Once that happens, people would likely sell their bitcoins and that will contribute to its volume in the market. I believe that the 21 million bitcoins in existence would just circulate until another type of cryptocurrency would dominate instead of bitcoin. Nevertheless, I highly doubt that it will disappear despite having many conflicts in the world (even if the government decided to regulate it).