It's really hard to predict what could happen in this world in 20 years. Bitcoin might not even exist anymore. If it would.. I guess it'd have a really great price to sell

i dont think it will disappear cause many are using it... but the price will get higher... eventhough the present rate is much stable but it will hit the sky with 2000$-10000$ in the coming 20 year....
Yup There is no symptoms like bitcoin is getting disappear from us and you can not hold your fiats for next 20 years also but at the same time you can save and hold your bitcoins for next 20 or even 50 years also. That is the power of bitcoin and it will get multiplied minimum thousand times in next 20 years may be more than you speculated.