I think one generation is about 30 years and working with that, will Bitcoin last as longb as we imagine?
Yes, don't look at the supply limit, but concentrate your attention on it value, bitcoin has come to stay, not for now, but as an alternative digital currency to fiat.
Some private keys are already lost and many more are getting lost because their owners died without passing then on or they simply lost them.
21 million supply is not a child's play in Bitcoin value and not in USD value, yet bitcoin remains the most trusted and profitable digital asset and investment for everyone.
Based on these possibilities, what do you think will happen in some decades when many of the private keys are lost?
Our own bitcoin will receive a share of those lost coins, this is why bitcoin is ever an increasing digital currency and asset.