Natsu would probably be very confused and sad at first. He's used to having Lucy around, and her sudden departure would leave a big hole in his daily adventures. He might try to convince her to come back immediately.
Gray might be a bit more nonchalant on the surface, but deep down he would also miss her. He might crack some jokes about her leaving at first, but as time goes on, he would realize how much her presence meant to the guild and to him as a friend.
Natsu would probably be really excited at first. He'd be all over the place, asking a million questions and making sure Lucy is okay. Happy would be right there with him, trying to help in his own little Exceed way. Erza would be very protective. She'd make sure Lucy follows all the proper precautions and would offer to train her gently so she doesn't lose her fighting edge during pregnancy. Gray might be a bit awkward at first but would soon warm up and offer his support, like helping with any heavy lifting around Lucy's place.
Happy would be sad and confused. He doesn't like to see his friends in trouble. He would fly around trying to gather information from different guild members. He would also stay by Lucy's side, trying to cheer her up. And all of her other friends in Fairy Tail would at least have some doubts about the decision. They know Lucy's character, and her sudden expulsion would make them question whether the guild made the right choice.
Lucy might be really surprised at first. But then she'd probably blush and say yes. After all, she and Natsu have a strong bond already.
Natsu might be really confused and sad at first. He's used to having Lucy around for adventures. But he would probably respect her decision in the end, knowing it's for the baby.
She might be initially shocked. After all, she would have trusted her friends a great deal. Then she could become very sad and withdrawn. She might throw herself into her studies even more as a way to cope, trying to distract herself from the pain of losing her friends.
She might be initially shocked and hurt. Hermione is a character who values her friendships deeply, so their sudden departure would be a big blow. She could spend some time in denial, not believing that they would actually leave her.
A possible reason could be personal conflicts within the guild. Lucy might have an issue with some of the guild's rules or how certain things are run. Juvia could be following Lucy for some reason, like loyalty or because she also has her own issues with the guild. For instance, if there are tensions between Juvia and other members over Gray.
The guild as a whole would likely mobilize. Erza would start formulating a strategic plan. She'd consider the strengths and weaknesses of Acnologia and figure out the best way to approach the situation. Gray would also be ready to fight, using his ice - make magic to support the rescue mission. They would all be united in their determination to get Lucy back safely.
One possible reason could be that she feels she has outgrown the guild. Maybe she wants to explore new magic on her own and believes the Fairy Tail environment has become too comfortable and is hindering her growth.
In terms of her relationship with Gray, there could be a new dynamic. If'si' reincarnated as Lucy, she might be more competitive with Gray, which could lead to some interesting interactions. Her relationship with the celestial spirits would also change. She could become more like a mentor to them, teaching them new things from her past life or experiences. Also, her relationships with other guild members would likely expand. She might form closer bonds with some of the more reserved members of Fairy Tail, bringing them out of their shells.