Pfft, death isn't necessary to evolution in the sense your implying.
Transmission of ideas and wealth - even societal restructuring doesn't require all the old people to first die.
Adapt or die. We cease to adapt and so we die. We're we as a species to overcome death individually, we would still collectively be bound by the same mantra.
Not that our evolution would stop - rather I think the opposite.
Assuming cellular commission is similar to a 30 year old and as healthy/mentally capable as a 30 something; so truly overcoming those obstacles - a 300 year old version of me would be better than the me now.
Taxi drivers brain composition changed by driving around London - I'll bet an extra 200 years will do something.
As long as our populace remain "Mentally Liquid" we will be fine - something 300 years of seeing and living constant changes should all but guarantee. Can't be yelling at the kids on the lawn for 200 years right?
I think elongation human life will be necessary in the not so distant future and I expect it to happen.