Of course, when the network connection is not available the addon package will not work. But there is solutions to solve this problem. Asobo could develop within MSFS to generate short duration public and private key pairs for encryption and decryption of the addon packages with included information about the gamertag and etc to prevent leakage.
Any solution will only protect the addon package for as long as possible until someone figures out the way to break the encryption system. But if correctly developed that shouldn’t be a problem for the near term.