With Offline Mode, you can take your system entirely offline for up to 7 days and still make use of all your premium content and subscription features. Once that time period is up, you will need to go back online momentarily in order to check for updates and re-validate your subscription status, but you can return to Offline Mode as soon as that check is finished.
If you don’t go back online after the 7 day period nothing bad will happen to your music. Everything within INSTRUMENT will still play back and respond to automation, but you won’t be able to load premium presets on new tracks until you go online.