I don't see a single benefit we could get as a species from the combination of aging + death that we couldn't get from death alone, provided the viable reproduc

I don't see a single benefit we could get as a species from the combination of aging + death that we couldn't get from death alone, provided the viable reproductive period weren't dramatically extended. Even then, we do a pretty good job of moderating the number of children we have, if we're confident they'll live, as other comments have said.