Nope, this is no existential question (although...). Everybody's talking about "When will Bitcoin die", but what if you die, and your family don't find your key, or don't understand it, or think it's only a useless sheet of paper with some code on it, or simply throw it away... Does this mean the currency's gone forever?
I find the possibility of this event rather realistic (yup I don't believe in eternal life), so that means that someday there might be 21M BTC but only 18M (and counting down...) is left in the market?
How long you want to keep your btc? I think you have a beatiful plan for it use. But remember, we're not live forever, Nobody. So by doing investment with this crypto, you need to tell someone you can trust, just told him/her, you have an asset in bitcoin, and you keep it in online wallet, and you have print it seed. So If you're gone, and dont have a time to use it, they will find and learn how to use it, because its your legacy.