Your offline are just that. They are Cached on the device for not connection needed. Think of it as a iPod .....
If you open it once a week the playlists will update if you follow certain ones, weekly, top hits, etc. But Anyone you created and added yourself will not disappear or go away.
If you open it once a week the playlists will update if you follow certain ones, weekly, top hits, etc. But Anyone you created and added yourself will not disappear or go away.