The aircraft in question was scheduled to fly LST-MEL-ADL-BNE and beyond that day, and carried many connecting pax destined for ADL,BNE and other places besides MEL.
The aircraft had enough fuel to hold for hours (literally) and chose to divert in consultation with OPS when the wx in MEL was obviously not fluctuating, well below landing minima, and at a time when it would arrive in ADL in time to maintain its schedule.
When the aircraft landed in ADL, the first aircraft had just managed to get into MEL, so if the flight had chosen to stay on the ground in LST until the fog had lifted the MEL bound pax would have not got there much sooner than PAX shifted onto a ADL-MEL flight after the diversion. The ADL bound connecting pax were very happy and the BNE bound ones were not much worse off. The LST-ADL flight burned 400kg more than LST-MEL-ADL would have, which is not bad considering 30 min hold, but then we did hold at FL240.
Well that was the plan, the aircraft departed knowing full well MEL was closed, gave the Weather Gods a chance to smile, but with a plan to minimise downstream disruption at a cost of inconveniencing a few.
Cheers
ps I am impressed by the contributions to this thread, as it is one of the more courteous and open minded I have read in this forum.