Re: Wonder when the NSA will notice this
They already know who it was and when. Plus if this is what I think it is, DSNET 2 and DSNET 3, which were the predecessors of what's called JWICS nowadays, he only killed the local instance. The Emergency Action Messaging system, NSA's CRITIC flash messaging system which has the next highest priority after EAM, and the key distribution systems for what you'd probably know as the "Launch Codes" are all separate anyway.
There are also multiple backup systems, like at Fort Meade, Fort Belvior, Norfolk, and possibly even the one at Raven Rock/Site R, one of which very likely took over until the system at the Pentagon itself came back up.
It was probably actually a good way to test continuity of operations planning in an unannounced sort of way and back then it was fairly important to do so irregularly. It'd aggravate the Joint Staff and the Chiefs if they were around (as well as HQDA HHC and the rest of the baboons around the JCS Tank for that matter) but mission performance wasn't likely seriously degraded.
Plus, back then AT&T managed the keying for the STU-II and STU-III phones outside of the Pentagon itself at their survivable facilities ("Project Offices" in AT&T jargon) outside of the Beltway so they could still pick up a secure phone and call DISA and/or the watch officer at the NSOC at NSA to see what was going on.