so I am a bureaucrat for the Grain & Mango's Center Wiki, https://grain-mangos-center.fandom.com, and my co-founder, Grain the Seawing, has been inactive for more than a month. Her most recent blog post was about leaving the wiki. How do we demote her?
Unless the user is problematic (and Wow! Be careful about handing out bureaucrat as easily as you do, troublesome 'crats are difficult to remove), Staff (contact Fandom Staff) will usually recommend leaving them as they are, especially after such a small period of inactivity. They may decide to return someday.
BTW, a bureaucrat can remove themselves. Have you tried asking them to do so?