For anyone who still wants to use this (or are curious about it), I found out this way to get the engine going solo after going offline.
1. Try to log in with the built-in account and let it fail (the credentials are stored in the event the master server comes back up I think)
2. Go to where you extracted the bulk of CraftStudio. There you'll find "userdata/CraftStudioClient". Launch the application of the same name
3. Once it comes up, the server manager also comes up. Connect via localhost (or 127.0.0.1 if you can) and you're in! So far I've only made an inanimate player character for my test project.
Optional: Replace the main shortcut with CraftStudioClient.exe for smoother functionality