When Sam Blake, a successful hitman, discovers he has a fatal disease he vows to never kill an innocent person again, but the only way a hitman retires is to sign The Agenda, a list of targets, and compete against other hitmen to see who can rack up the most kills…so Sam decides to eliminate the competition.

My point was why does he have to partake of "the Agenda" when he's a dead man walking?

Whatever.

>>A threat to his family? His kid?

That might work. A la "Breaking Bad". After diagnosed with almost certainly fatal lung cancer, a milquetoast chemistry teacher decides to cook meth to provide for his family after his death.

My point was why does he have to partake of "the Agenda" when he's a dead man walking?

Whatever.

>>A threat to his family? His kid?

That might work. A la "Breaking Bad". After diagnosed with almost certainly fatal lung cancer, a milquetoast chemistry teacher decides to cook meth to provide for his family after his death.

The hook that makes this interesting is not the fact that he's dying, but that in order to get around his "no more killing innocents" vow, and yet still partake in the "The Agenda" he decides to kill all the other hitman (because, as hitmen, they are not innocent).
I would find a better motivation than that he is already dying, because as dpg suggests, if he's dead anyway, why do we care if he makes it out clean or not? Give your protagonist a different, but just as primal and high stakes reason, for wanting to get out. A threat to his family? His kid?