One common theme is his growth as a sorcerer. Many fanfics focus on how he hones his skills and becomes stronger. Another theme is his relationships, like his friendship with Yuji or his complex connection with the Zenin family.
There's a fanfic called 'Megumi Fushiguro: A Different Path'. In this, the author takes Megumi on a completely different adventure from the original story line. It's really interesting to see how his character develops in this new scenario. Also, 'Megumi's Hidden Powers' is a fanfic that uncovers some potential powers that Megumi could have, which makes for an exciting read.
As of the latest chapters I've read, Megumi is still alive in the manga. Usually, such major character deaths are significant plot points and would be well-publicized if they occurred.
Typically, megumi fanfic often focuses on his personality traits. His stoicism and determination are often highlighted. For example, in many fanfics, his unwavering resolve in the face of danger is a central theme.
Well, Megumi's story in the manga was full of twists and turns. She had to overcome various obstacles, and there were also some unexpected developments in her relationships with other characters.