Some fans might be really shocked. They are used to seeing Artemis as a more or less benevolent figure, so this sudden betrayal would be a big twist. They'd probably be eager to read more to find out the reasons behind it.
On the other hand, there could be fans who are interested in seeing the drama and conflict that would come from this. They might enjoy seeing how the characters would deal with such a complex and emotional situation. It could also open up new ways of exploring the personalities of Percy and Artemis.
Initially, Percy is likely to be heartbroken. He thought he had a certain relationship with Artemis, whether it was friendship or respect. So when she betrays him for Orion, he may go into a state of self - doubt. He could wonder what he did wrong and start to isolate himself. But as time passes, he may gather his strength and decide to face Artemis and Orion head - on, to either regain Artemis's trust or show her the error of her ways.
Well, she could betray Percy by revealing his secrets to his enemies. Maybe she's forced to do so under some kind of magical compulsion or threat.
At first, Percy would likely be angry. He has faced so many challenges with the belief that his father was on his side. The betrayal would make him feel like all his efforts were in vain. He could lash out, perhaps even using his powers in a more reckless way. But as time goes on, he might start to question if there's a deeper reason behind Poseidon's actions and try to find out the truth, especially if he still has friends who believe in him and encourage him to look deeper.
Percy would be extremely hurt. Sally is his mother, and her betrayal would shatter his world. He might initially go into denial, not wanting to believe that she could do such a thing.
Artemis would be in shock initially. Given her status as a powerful and independent goddess, the idea of being forced into marriage is unthinkable. She would likely try to use her divine powers to break free from the situation. If she can't do it immediately, she might start to negotiate. She could offer other things in exchange for her freedom from this marriage. And if Percy shows any sign of taking advantage of the situation, she would not hesitate to put him in his place.
Percy would probably be really confused at first. I mean, one moment he's a normal demigod and the next he's a jackalope. He'd likely try to figure out what happened and how to change back right away. He might be a bit frustrated with Artemis for doing this to him without much warning.
It could be that Artemis betrays female Percy out of a sense of duty to the gods' code. Suppose there is a rule among the gods that female Percy has unknowingly broken. Artemis, being a strict adherent to the gods' laws, decides to take action against her. This could involve setting traps or leading her into dangerous situations, all in the name of upholding the divine order.
In the long run, Percy might grow from the experience. He could become more cautious in his relationships and less trusting. Or, if there's a chance for redemption in the fanfic, he might be open to forgiving Annabeth if she shows true remorse and has a valid reason for her actions. But initially, it would be a very difficult and emotional time for him.
Percy could lose trust in the gods completely. After Artemis' betrayal, he might feel that he can't rely on any of them anymore.