You probably need to distinguish what type of offline use you’re talking about…
- There’s the desktop apps which support Downloading content for offline use.
- There’s the mobile apps that support Mobile Sync
I’m not aware of any restrictions as the ones you described. Then again I haven’t been offline for several months.
Personally I’d go with downloading movies using the desktop app. This way you can still access them in the configured download folder (see support article above) even if Plex might get some hiccups after some time.
There’s an article on how to run Plex without an internet connection – this is mostly focusing on operating a Plex Media Server in an offline context (e.g. if you have access to a WLAN that’s not connected to the internet). Still it might give you some insights in potential caveats… or give you some inspiration for an own “offline server” for wherever you’re stuck for 2-3 months without internet connection.
