If the FBI were to dig....which I doubt they have incentive to do so...I think they would find that the prior-planned event was a Breslan-type event where a group (more than the husband/wife team) would take over a school cafeteria with several hundred potential victims.
It is very possible that this may have been the case. Maybe, just maybe, the "heated discussions" with his co-worker set off his desire for Jihad so highly that he couldn't help himself, and thus circumstantially prevented, hopefully, and not simply delayed, an American Beslan event?