Ah, but which ending?
Yeah, there are multiple endings to Blade Runner. In the original release, Gaff spares Rachael's life, allowing her and Deckard to escape the nauseating confines of Los Angeles. They drive away into a natural landscape, and Deckard informs us that despite what Gaff had said ("It's too bad she won't live. But then again who does?"), Rachael didn't have the built-in four-year limit to her lifespan that the other replicants had. So, somewhat surprisingly, everything wound up okay. Ish.
And that origami unicorn Gaff left behind? Eh, that was just a sign that he'd visited the apartment and decided not to kill Rachael.
In the endings to some of the other versions—like Ridley Scott's "Final Cut"—the implications are different. Deckard has a unicorn dream sequence earlier in the film, and Gaff's silver paper unicorn at the end signifies that he is aware of the content of Deckard's dreams because they're implants… meaning that Deckard is really a replicant. Ridley Scott said this is what he intended, but one of the screenwriters, Hampton Fancher, said he considered Deckard to be a human, though he wanted some ambiguity.
In these versions, we just see Deckard and Rachael get into the elevator. We don't know if they'll even get out of L.A. alive, and no voiceover cheerily informs us that Rachael has a special, lengthened lifespan. The "Final Cut" and "Director's Cut" end on an uncertain and ambiguous note. In fact, if Deckard is a replicant, then it may very well be that his lifespan is just about up, too.
Also, we should probably address Roy's death scene, since it's the climax of the movie, if not the resolution. Roy unexpectedly shows mercy towards Deckard, sparing his life even though Deckard was just trying to kill him. When Roy dies, remembering the amazing things he's seen in his life, he recognizes the full value of human life—his and Deckard's. He dies holding that value supreme, while poignantly considering his own mortality: "All those... moments will be lost in time, like tears... in rain."
Witnessing Roy's death changes Deckard, who acts as an enlightened witness. It transforms Deckard from being a blade runner to being the guy who runs away with a replicant to try to live a life of peace.