Perhaps she has a new mission or calling that takes her away from Camelot. It could be something related to the greater magical world. For example, there could be an ancient magic that is in danger of being lost or misused, and she is the only one who can save it. Since Camelot has been rather unkind to magic in general, she might feel that she has to leave to fulfill this important task.
Long - term, Arthur may start to question his own beliefs. Merlin leaving could make him re - evaluate his stance on magic. If he realizes how much he has lost without Merlin, he might start to think that perhaps the way magic has been treated in Camelot is wrong. This could lead to a change in Camelot's laws regarding magic in the future, but it would be a slow and difficult process as he has to overcome his own prejudices and the long - held views of the court.
A plot might involve Merlin leaving Camelot to seek greater magic knowledge. He has learned a lot in Camelot, but there are still secrets about his powers and the old magic that he can't uncover there. So, he sets off into the unknown, leaving behind his friends and the life he has known. This could lead to him encountering new magical creatures and learning ancient spells that he can later use to help Camelot in a time of great need.
Well, don't forget about Goodreads. Although it's mainly known for book reviews, there are groups and discussions about fanfiction too. You could start a thread asking for 'Camelot watches fem Merlin' fanfiction, and chances are someone will point you in the right direction. Additionally, some Merlin fan communities on Discord might have channels dedicated to sharing fanfics like this.
Gwen could also be a very sympathetic character. If Merlin leaves, she would be one of the few who truly understand how much he has done for Camelot. She has seen his selfless acts and his loyalty. She might be heartbroken that he has to leave and feel powerless to stop it. Also, she has to deal with the potential loss of a great ally in the court and a good friend. She might struggle with trying to convince Arthur to let Merlin stay or find a way to bring him back.
One great source could be Archive of Our Own (AO3). There are numerous fanfictions there. You can search for 'Camelot watches fem Merlin' and it'll bring up a bunch of stories. Some might focus on how the characters in Camelot react to a female Merlin's magic, or her relationships within the Camelot setting.
Many fanfictions show Merlin's magic as a hidden force. For example, some stories depict him using magic subtly to influence events or protect Arthur without being detected. His magic is often portrayed as a double - edged sword. It can save Camelot but also put him at risk if discovered.
One great Camelot Merlin Igraine fanfiction is 'The Legacy of Igraine'. It beautifully weaves the relationship between Merlin and the memories of Igraine. It shows how Merlin discovers more about Camelot's past through Igraine's story and how it impacts his present role in Camelot. The story has vivid descriptions and really makes you feel like you're in that magical world.
They could have an adventure where they help Camelot defend against a dark sorcerer. Harry's combat magic from Hogwarts would be useful, and Merlin's knowledge of Camelot's magic and its secrets would be crucial. Another adventure might be to find a lost magical artifact that is important for both Camelot and the wizarding world. Along the way, they might encounter magical creatures unique to Camelot that Harry has never seen before, like the Questing Beast.
In some fanfictions, Camelot guards protect Merlin by being constantly vigilant around him. They might accompany him on his errands outside the castle, especially when he's in areas known to be dangerous. For example, if Merlin has to travel through the forest to gather herbs for Gaius, the guards would go with him to fend off any bandits or wild animals.