Though the theatrical "happy ending" seems to diminish Blade Runner's intended themes a bit, the conclusion still could be summarized as the inevitability of death and the dehumanization of technology.
What does the unicorn at the end of Blade Runner mean?
The unicorn itself is, of course, a mythical creature steeped in mystery and its uniqueness embodies the kind of individuality that Deckard believes will satisfy his anxiety. It, therefore, serves as a metaphor for Deckard's quest for existential authenticity and a vehicle on which he can pin his hopes and aspirations.
Blade Runner raises the question of whether a constructed being should count as a person. In the movie, replicants lack legal rights and are not regarded as human. Similar questions are raised in later unrelated works such as Her and Westworld.
Gaff is showing Deckard that he knows about the unicorn dream that Deckard has had; he is showing Deckard that he is privy to Deckard's thoughts and memories. This would only be possible if Deckard were a replicant with implanted memories.
K then used the situation to fake Deckard's death, saying he drowned. Afterwards, he took Deckard to Stelline Laboratories, urging him to meet his daughter. As Deckard went into the lab, the severely injured K laid down on the steps outside and succumbed to his wounds.
Because of this memory, K became convinced that he was Rachael and Deckard's child, but was eventually informed by Freysa that he was not and that the child was female. With this revelation, K soon determined that Stelline was the child. K took Deckard to Stelline's lab as she interacted with a snowfall hologram.
Prior to the events of the film, Deckard's replicant lover Rachael became pregnant with his child but died in childbirth. Deckard was forced to leave the child, a girl, with a replicant freedom movement and scrambled the child's birth records to protect her before disappearing.
Gaff could have caught Deckard and Rachael, but his sympathy for their cause influenced him to allow them to escape, and that's exactly the type of person Cal was looking for.
On a thematic level, it represents K's yearning for humanity, a soul, and freewill. He wants to be "born, not made." Also, like the film itself, the wooden toy horse evokes nostalgia. It turns out that the wooden horse memory is Ana's and that it was embedded in K's memory as a safeguard to hide her identity.
Upon meeting his "maker," Roy demanded an extension of his life and a brief discussion followed. Infuriated at Tyrell's inability (or unwillingness) to grant him longer life, Roy crushed Tyrell's skull and then murdered Sebastian before fleeing.
The anti-villain is dying in the middle of fighting Deckard, with his pale hand exhibiting signs of shutting down as Roy's replicant body gives up on its existence. To keep himself in the fight a little longer, Roy jams a nail into his hand.
By its conclusion, the film suggests that one's ability and willingness to perceive systemic social inequality is the true measure of humanity. Blade Runner trains us into awareness of flawed social hierarchies by repeatedly emphasizing eyes and connecting them with perception beyond the physical.
"I've seen things you people wouldn't believe. Attack ships on fire off the shoulder of Orion. I watched C-beams glitter in the dark near the Tannhäuser Gate. All those moments will be lost in time like tears in rain.
The big twist in the final act of the movie is that K isn't the son of Deckard and Rachael at all, but just another cog in the machine that might lead to the child's discovery.
The film reveals that Deckard was able to conceive a child with Rachael, and this was possible because she was an experimental prototype (designated Nexus-7), the first and only attempt to design a replicant model capable of procreation.
However, he later learns that, even if the memory is real, it was not his own but Dr Ana Stelline's. Through her work, Dr Stelline shared her memory with K, and this allowed him to understand what it was like to walk in her shoes, but most importantly, to believe himself a free, loved replicant.
During the final fight with K, after subduing him, she smugly kissed him and retorted "I am the best one!", as if trying to prove her superiority over not just K, but all other replicants, further hinting at her deep-seated insecurities that she kept well-hidden.
The horse, with the inscription "6.10. 21", establishes the connection between the dead female replicant who gave birth and died on 6.10. 21, and K himself, implying that the memories were not in fact "implanted" but are rather genuine after all.
Blade Runner 2049 revealed that Rachael was the first replicant to get pregnant. Deckard is the father, and it's suggested - though never stated aloud - that the only way a replicant could get pregnant is by another replicant.
Rachael wanted to further explain, but Deckard cut her off to recall to her the memories of her childhood; informing her that he was only aware of her memories because they were imprinted. Deckard explained to her that her memories were false due to their connections with Tyrell's niece.
To show Deckard that Gaff knows what he is thinking he says “it's too bad that she won't live”, with the “she” clearly referring to the female nexus that Deckard has fallen in love. His mock regret also alludes to the fact like Batty; the female Nexus too is on a limited life span.
Ana Stelline (Carla Juri), who is Deckard and Rachael's daughter but has no idea of this and now works as the world's best memory fabricator. We don't know if she planted that memory in only K's brain or in the brains of hundreds of replicants, hoping one of them would follow this message in a bottle. Maybe others did.
At the lab, Stelline was confined to a room blocked off completely by a transparent screen through which she could speak to clients. This was due to a compromised immune system, a condition that also prevented her from emigrating Off-world with her adoptive parents.
