There is no such guarantee, and if Bitcoin gets overtaken by new technology - something which appears to be already happening (given how much Bitcoin's market share dropped in a mere few months!), they will very likely end up holding the bag.
So what is your suggestion? To sell all bitcoins we have? That sounds like advice from someone who want to buy some cheap bitcoins, nothing more.
None: everyone should make their own decisions.
Your response is one of the things I've been worried about most in this board since 2013: the lack of (self-)criticism to challenge certain viewpoints, and the tendency to immediatly paint those that utter it as people spreading FUD, or that have some other interest that involves seeing Bitcoin die. It has enhanced the cult-like behavior here, as valid criticasters at some point get tired from talking against a brick wall.
Hodlers are nothing but a victim of the climate it creates.