Not the OP but I believe they are referring to the idea that if longevity research causes lifetime extension to be possible, then some folks think they can then avoid age-based death entirely. I think that the crux of the argument is that once we find "THE reason" why we age and if we can halt/end that process then we have beaten senescence.

I personally think this view is too simplistic about how our bodies work and overly optimistic that we a) won't hit other limiting factors that aren't hit today by ~100 and b) that interventions to stop senescence won't have unexpected side effects.