Is there any way to get an Argentine victory in the Falklands war? I doubt that the Argentines can win outright militarily, but is it possible for them to provoke a casualty pit that drains British public support for the war? Perhaps there is more domestic trouble for Thatcher?
Is there any way to provoke a British invasion of Argentina proper, perhaps if Argentine forces on the island can dig in beyond the British's hope of dislodging them? Such a war could easily lead to high enough casualties for the British public to eventually demand cutting losses...
Your POD can involve changes in Argentine and/or British domestic politics--to the point where the war doesn't look much like OTL--but if you don't, what does such an outcome do for the politics of each country? Does the junta last longer? Does Thatcher's gov't fall?