Sure, lots of philosophers talk about lives barely worth living, and what constitutes the line. Lots of public health researchers work on metrics for quality-adjusted life years, and increasing longevity is useful only insofar as it increases QALY's.

But I really do expect most measures which increase population longevity to increase population QALY's. The conflict between hypothetical immortal tyrants and immortal coup-conspiracies would only be a small part of this; material conditions and overall societal wealth would weigh much heavier on the scale.