This is actually an interesting question, given that it must be quite a rare occurence. Technically I imagine that the Airlink crew, if they had only planned for a normal alternate that was subsequently denied to them, would have to declare a fuel emergency and start planning to land at any airport that is most conducive to ensuring the safety of their passengers lives. Taking this further, the worst case scenario would be any airfield they chose then being physically blocked (tanker truck in the middle of the runway or something like that), in which case the Madagascan powers that be would have the potential blood of quite a few people on their little paws. Once they're into the 'emergency zone', they can (in my mind at least) do pretty much whatever they decide is most likely to save the passengers and aircraft. They may of course all be arrested once they taxi in of course....a real low blow by the authorities there, and I'm just talking safety, nothing political. Good job those Airlink guys carried that fuel I guess. I have no idea how much of an idea they had that this would happen, but good going nonetheless.