[Oh, spoiler warning by the way.]
io9 compares early Blade Runner scripts, including one that just recently surfaced. In all cases Deckard realizes he's a replicant, and in at least two versions he blows Rachael's brains out against a snowy backdrop. [Dang. And you didn't think that film could get any darker.]
Deckard finds Gaff staking out his apartment, and almost shoots Gaff. But Deckard says (in a voice-over!) that he's tired of pulling triggers. So instead Rachael and he sneak out and go out to the countryside. Rachael makes Deckard pull over because she's never seen snow before. They talk about Roy Batty, and how he made Deckard realize every moment is precious. Rachael says it's the happiest day of her life, then she begs Deckard to shoot her. He does. Then he drives off, realizing it's too late for him to get away. "They wouldn't give me papers for the Colonies even if I wanted them." He wonders who designs "the ones like me."