I think death is inevitable in the way that in order for further life to continue, there must be death. The reason we love and experience things and go do stuff is because we know we have a limited time in this earth. We make way for the new just like the ones who came before us made way for us.
But then it doesn't sound like you think death is inevitable so much as that it's good.
It looks like you're making two different claims:
1. If you lived forever, there wouldn't be any reason to do anything.
2. Living forever isn't compatible with letting new people be born and live their lives.
To your first point: if you learned you were going to liber forever, would you stop spending time with your friends and family? Would you stop enjoying the time you spent together? I really don't see why you would. You might choose to put off some major life transitions, like having kids or starting a business, but would you put them off forever? If you really would put them off forever, are you sure that it's something you want to do, or do you just feel like you are supposed to do it? Is it a bad thing to let your twenties last 40 years, and only then settle down, because you know you have all the time in the world?
To your second point, I could go on about how there are a number of ways to make immortality compatible with new life, but sure, let's say that there isn't. Then the advent of immortality would be a radical change to the present order of the world. But would it be a bad change? The circle of life is beautiful, but the prospect of no one ever dying ever again is, I would say, good on the scale required to say that it might well be worth sacrificing the potential for new people to enter the world.
I think of it as needed for the species and not for the individual. My and your values currently living have been shaped by our parents and people who we have met. These people have been influenced by the fact that death is inevitable. Our human history has had the inevitability of death looming over it since we went from being non-life to life. I don't think we can judge this based on what I currently would want for myself.
My views are shaped around the fact that I can die. And if I woke up tomorrow knowing that I cannot die, I would still have those deeply ingrained values in me.
I'm more worried about the effect on the human species. How would my great great grandchildren act in the world knowing nothing of death or the fear of during from old age? I'm not so sure it's 100% a positive thing and it has the potential to be a very negative thing. Worse than what we have right now.
This is all very fascinating and it's really interesting to speculate though. There's probably just as many arguments in opposition as there are in support.
