Yes, the HMS hub can be used without a subscription, however there is a significant loss in functionality. Without a subscription it no longer functions as an alarm system and functions more as a contact and motion sensor hub.
See this: Home monitoring without subscription?
As for unplugging it, transporting it and not using internet… No.
Without a subscription the unit has no alarm, only push notifications to your phone when a sensor detects. Without internet that functionality is lost.