While I am a fan of SMBC, in this case he's not doing existentialism justice (or not understanding existentialism). Existentialism is not the same thing as deathism. Existentialism is about finding meaning and responsibility in an absurd existence. While mortality is certainly absurd, biological immortality will not make existential issues go away. In fact, I suspect it will make them stronger..

edit: on the other hand, "existentialist hokey-pokey" is both funny and right on the mark!