If you live as if you'll die, and you don't, you'll have a much more interesting life, because you took advantage of it thinking you're living under the Sword of Damocles.
If you live as if life extension will keep you going, and it fails, you'll have a short, boring life, full of things you put off until it was too late.
Those are the extreme values of the matrix; if you work through the rest, I think you'll find that the most utility is always gained by living as if you'll die eventually.
(Living as if you'll die tomorrow is romantic and all, but it would prevent you from working towards any goal which takes more than less than a day to complete. It could also land you in prison, deported to a less-pleasant foreign country, or both.)
I guess first we'd have to define "fullest." Your meaning and mine are probably completely different. If all you want is to be in that happy place, well, ... good luck. I bet Elon Musk, Steve Jobs, Jeff Bezos, and Bill Gates have a different idea about what they want/wanted to accomplish with their lives.
Think about it game-theoretically:
If you live as if you'll die, and you don't, you'll have a much more interesting life, because you took advantage of it thinking you're living under the Sword of Damocles.
If you live as if life extension will keep you going, and it fails, you'll have a short, boring life, full of things you put off until it was too late.
Those are the extreme values of the matrix; if you work through the rest, I think you'll find that the most utility is always gained by living as if you'll die eventually.
(Living as if you'll die tomorrow is romantic and all, but it would prevent you from working towards any goal which takes more than less than a day to complete. It could also land you in prison, deported to a less-pleasant foreign country, or both.)