Well - not only authorization is needed, but also ALL the install files you need to install the product. Only the install and maintenance center would not work, because it depends on huge files that have to be downloaded from some server.
So - The users should not only have an off-line authorization mechanic, but also the possibility to download all installation files from their software and store them locally in a safe place, in case Gibson goes belly-up and all file servers are shut down. Think a bit how Camel Audio gave access for a limited time to their full Alchemy installer files for registered users. What good does an off-line authorization if you do not have a program to start with?
So - by all means off-line authorization, but that is not enough