I think the reason the owl was left in the cage is cuz the rest of the harry decoys had fake owls that couldn't fly. I think harry exploded the sidecar so it wouldn't crash into some hapless muggle taking an evening stroll, plus the death of the owl removes her as a plot device to contact the rest of the Order (or Ron) while Harry is on his quest. The patronus charm takes the place of that. Other than that, your review is very insiteful. Good job!!