You're talking as if this would be a war between states, with the Geneva Convention rules applying
From the Argentines point of view they would be just reasserting control over a rebel province, the Geneva convention won't apply
It doesn't matter what the Argentines' "point of view" is! The islands are recognised in international law as British territory and therefore any conflict between Argentina and Britain in the Falklands would be a state-on-state conflict and the Geneva conventions would most certainly apply. Even if the Argentines overran the islands once again, a state of conflict would still exist and the conventions would continue to apply. The conventions would only stop applying as and when Britain ceded the islands; then, as you say, any Argentine security activity would be 'internal'.
Chances of us ceding the islands without a fight? Zero!