One way or another that operator believed strongly enough there was a use for determining the position of the mortar team, strongly enough that he put down his primary weapon and lite the target up.
Then he was left to hang out to dry and died.
I guess the people with no experience in this cannot grasp this inescapable conclusion that all of us who have "been there, done that" seem to be reaching. There must have been a fire mission planned - somebody wanted coordinates - (even if people at the annex were designating the target) - I have more or less rejected the idea it was for US or Allied (Libyan?) artillery, but there are tons of other options as you have suggested. CIA has their own drones, USAF and USN had assets that could have been parked for support (at least by that time, if they reacted quickly), and USA has armed drones, although it is unlikely any were in range of Benghazi. Any combination of fast movers, drones, missiles, TLAM, whatever, could have used the targeting information.
The fire mission never got clearance. That is the only conclusion I have not rejected.
The only other possibility (that my limited brain can conceive, anyway) is that the GLID user was told (or assumed) assets were available to use the information in a short time window (3 to 5 minutes). Whether or not this was confusion, misinformation or worse can be subject to speculation. After that, I'm out of ideas.