My buddy sent me the rule on homers. He also said there is no specific rule covering ground rule doubles so he'd call the game when the first runner touches home. After that, it's a scoring problem if anyone wants the extra RS/RBI/whatever. As far as umpires are concerned, the game is over.
(c) If the home team scores the winning run in its half of the ninth inning (or its half of
an extra inning after a tie), the game ends immediately when the winning run is
scored. EXCEPTION: If the last batter in a game hits a home run out of the playing
field, the batter-runner and all runners on base are permitted to score, in accordance
with the base-running rules, and the game ends when the batter-runner touches
home plate.