If you leave the instance before the boss dies, doesn't that remove you from the "can loot" list?
Similar to if someone dies in a boss fight, releases, tries to enter the instance but gets the "encounter in progress" error, is bounced out alive. And is unable to have any loot given to them by the Loot Master, or loot things such as badges themselves.
I've never been dick enough to try something like this, so I don't know =P