I just tested this and confirmed that if you build, file, get brief. You don't have to activate it, just file it. Then with no internet, you can go back to Flight Plan -> Online Filing -> Options and then select View Briefing. It should be there for you to view even when offline. If you File and do not get a briefing, I'd image it would not have one to view.
I'll confirm this with Brian and Walter as this brief is from LMFS and is linked to the filed flight plan. It's seems if you do not file it, and just get a brief, it is not retained as a brief for an unfiled plan. This may be a limitation of LMFS or such. More to come.