Curate, connect, and discover
If there was a love triangle between Hayley/Klaus/Caroline in The Vampire Diaries, who do you think Klaus would prefer?
Let's consider this scenario for after he sleeps with her. I am certain Klaus would choose her, it would take time but he would definitely choose her not because she is pregnant with his child but because eerily enough she accepts him and understands him without judgement, is his mirror in fact and it's not just a one sided thing, they both complete each other.
Caroline "Klaus is root of all evil until I need something" Forbes would manage to string him along only so long. If he wasn't so intent on getting back at Tyler and so caught up in the thrill of playing hard to get he wouldn’t look at her twice. Caroline has on multiple occasions betrayed his trust, used his affections for her own gain and demeaned and disrespected him. Let's be real it would take Klaus two months tops, my bet is one really to get bored of Caroline, (when I say bored I mean irritated, annoyed, disappointed at Caroline).
Yes Klaus would initially be furious he lost precious hybrids due to Hayley's schemes but he would come to admire it instead.
Her ambitions to do everything under the sun and otherwise for the sake of mere information on her family(she was born to be a Mikaelson), her exceptional cunning, wit and survival instincts all stemming from roots of abandonment leaving her to face the world alone quite like his very own and her strength and perseverance despite it? It would awe and mesmerize him, I would say he would be falling for her so fast and so hard given their compatibility and chemistry.
Plus Hayley has what it takes to stand on equal grounds with Klaus Mikaelson and she would also get along swimmingly with his family (and if he have any evidence to go off of from The Orignals she would even unite them like never before). Caroline would be nothing short of a frivolous and insignificant distraction in the grand scheme of things between Klaus and Hayley.