Permanent casts wouldn't really work on wuwa. All the getting close to lupa plot/date wouldn't work the same if you had multiple third wheels following, every important decision would become a meeting bloating the length and slowing the pacing (or worse, taking the limited time of the main plot and characters that aren't part of the main cast and therefore get even less). Old characters should definitely not disappear, but they can work without being rover party/orbiters, like carthetyia, phrolova and cristoforo this patch, all doing their thing independently and meeting rover when it makes sense.