His analysis of the raids make good/funny reading - and he probably has some valid points - fuel usage - and the SHAR could deliver bombs more accurately - only needed to put 2 on the runway and it would have beaten the Vulcan! - still cant imagine that a single Iron bomb (or 2) would keep the runway out of action for long (and it didn't by the looks of things).
Although there is the Strategic argument to justify the Black Buck raids - even if Mirages operated CAPs over the Islands I fail to see how that would have been a disaster. It would have made things more challenging certainly - but the Mirage IIIs did CAP on the first few days and were hopelessly outmatched - poor missiles, no countermeasures, and poor tactics (fighting/welded wing).
Wiki (from the official FAA Magazine no less ) mentions that Mirage 3s were still used as decoys during strikes by the Argentine FAA so they were not all withdrawn after the raids if thats the case.