Bitcoin is not only about cryptocurrency, but also about blockchain. This technology is used a lot and will be used in spheres we can't even imagine now. Besides, there are many other cryptocurrencies, so we don't need to focus only on bitcoin.
Yes youre right, Blockchain might be very useful in the future and will be used for a lot of things that we dont even know now. And Im also very sure that Bitcoin wont end in the future after all coins are mined, they will not allow it to end just like that. During that time demand will play the bigger role in determine what will be the price, when there is higher demand the value will increase and when there is less demand the value will decrease.