This seems kind of sad, and i don't mean that to be mean or condescending.
For me, life only has value BECAUSE it's a temporary thing. You're given a limited amount of time to leave the world a better place than you found it.
Death is a necessary part of the life experience...without it theres no room for other things to be born and grow and have their own unique experience.
When my time is up i prefer to think i made the most of my time that i could with the limited resources i had. Letting go doesn't frighten me at all.
Endlessly existing into infinity with no actual goal or being reincarnated millions of times over and over just sounds tiresome, and more like a fantasy to keep away the fear of nonexistence.
I mean, yeah its sad, but I also don't care very much for giving others new experiences.
I'd be fine existing for no reason because I don't really
need a reason. I like being me, I like my own mind, my own relationships, my own experiences. I don't want to define my life by how I could affect others, I want to define my life by experiencing as much as I can. And a definitive end limits how much a person can really experience.
Hell, I'd be 100% okay with all of humanity becoming sterile and undying right this moment, because regardless of new voices, life still changes. When people are bored they experiment, find new hobbies, develop new skills. Every century that passes, each person would likely have developed an entire new set of likes and hobbies and ambitions, and I find that much more interesting than the idea of the cycle of life.