How many Allied casualties occurred in the Pacific and Atlantic theaters of operations after the cessation of hostilities?
Well, it comes down to whether you mean casualties from fighting or by accidents. I'll assume you mean fighting, but I'll include both. Casualties did occur in both theaters after hositilites "officially" ended. I don't have any specific numbers, but I can tell you that many more happenend in the Pacific, due to fanatical Japanese soldiers, who in places like New Guinea and the Philipines, refused to surrender and continued to harass and take pot shots at Allied personnel. The last ones were captured in the 70s or so. While I'm sure such a thing might have happened in the Atlantic theaters, German soldiers were far less fanatical and by 1945 were more or less happy to surrender peacefully (at least to the US/British!) As with any war, accidents do tragically happen (car/plane crashes, barfights, etc), so I'm sure a few soldiers survived the war, only to die afterward from something else before going home.