Killing should work for many tissues, especially those whose cells still divide. But for some tissues it is problematic. Killing senescent cell from muscle would make the whole muscle fiber to break. Killing senescent neuron could lead to loose of some cognitive or other function. So part of dealing with senescent cells is to modulate them so they do not vomit senescence associated secretary phenotype (SASP) which is quite annoying to other cells. Ultimately, we could rejuvenate senescent cells so they would work properly, but that seems much harder than other options.