Just my two cents...   I'd like to propose that if Mavis is no longer with the group, it might make more sense for her to go with the gnomes, to explain her leaving.  While the rest of us, having no real investment in going with the gnomes, head off with the kobolds guiding us.  Mavis was the one most invested in taking the gnome's side, so it would seem to be logical, without having to write her 'poofing' away.