Dean would probably be extremely confused at first. He might stand there, staring at his car with a bewildered look on his face, muttering things like 'This can't be real'.
Dean might also be angry. He'd be thinking about who or what could have caused this strange situation. He'd start investigating, asking around in the supernatural community he's a part of, and be determined to find a solution while also being frustrated that his beloved car is in such an odd state.
One possible plot could be that in a world of magic and mystery, Dean's car, which has some sort of enchanted spirit bound to it, starts to exhibit strange behavior. The car begins to glow and hum, and soon enough, there are signs of 'pregnancy' like a warm, pulsating energy from within. Dean has to figure out how to deal with this situation, perhaps seeking help from a local witch or wizard who has knowledge of such strange phenomena.
This situation in fanfiction can add complexity to Dean's character. When he is in a dominated role, it allows for a new perspective on his reactions, emotions, and relationships. It could also suggest that he has qualities that can be both strong and yielding, depending on how the fanfiction is written. For example, it might show his adaptability in different situations, which could be an interesting addition to his character portrayal.
Dean would probably be very protective. He's always been the big brother looking out for Sam, and with Sam as a kid, that instinct would be even stronger. He'd be constantly worried about Sam getting hurt and would keep him close at all times.
The other hunters in the Supernatural world, like Bobby if he was still alive in the fanfic, would also be worried. They'd offer their expertise and resources to help Dean. Bobby might give Sam some advice on how to take care of Dean while he's unconscious and how to find the culprit.
Well, in the context of 'dean gets dominanted by female fanfiction', it can really transform how we view Dean. In the original material, he might have certain characteristics that are associated with being strong and in control. However, when fanfiction places him in a dominated situation by female characters, it shows that he can be in a position where he has to rely on others or be influenced by them. This can make him seem more relatable to some fans as it shows that he has his own insecurities and can be affected by the actions of others, just like a real person. It also might make some fans appreciate the flexibility of his character in different fictional scenarios.
Some fans would be extremely shocked and heartbroken. Dean and Castiel have a very complex and beloved relationship in the fandom, so seeing Castiel kill Dean would go against what many fans hope for in their relationship. They might be very vocal about their disappointment.
He might be jealous. Dean could see Ginny's interest in Harry fanfiction as a sign that she is more interested in Harry than in him.
Their relationship might become more intimate as they share this unique experience. They would rely on each other more for emotional support.
Sam would probably be very protective. He has always been there for Dean, and now with a new addition to the family in the form of a baby, he would see it as his responsibility to keep the baby safe. He might also be a bit of a mentor, teaching the baby about the world of hunting and how to handle different supernatural creatures.
Yes, there are some out there. You can start by looking on popular fanfiction websites like Archive of Our Own. Just search for 'dean and elena pregnant' and you'll likely find a variety of stories with different takes on the concept.