Plot device cliffhanger, new trend to leave open ended but heavy implications and leaning on killing her . The whole close the door first was a plot device to end the flick with you talking about it later, to leave a mark on you, vs carry the logic of the story on.

If the point was to end her life, robot knows no one would hear, no need to close that door , and, no reprogramming of human minds element mentioned, or alluded to, so her use was over, maybe.

Robot AI would need daughter to trust the bots till kids raised , so killing swank would be counter productive unless the body was destroyed, leaving daughter to guess she left.

Ending was entirely a plot device for entertainment and shock value with What If factor add. If you follow the logic, the bots would live in harmony with new breed of humans, feeding them corn, and staying out of sight once tribes started making large cities etc. The bots are implied with a prime directive they themselves or a human programmed long ago that over reached it's goal, did the Skynet wipe and start over thing. No malicious intent for future human race , but definitely a threat to the recently current humans.

He AI learned thru daughter, and swank, that it will take many generations of new humans to get a stable group not emotionally compromised.