I just opened an admiral chest from the conquest event, and when I opened the chest, the client locked up and I couldn't do anything other than click on the UI confirmation window (verify to open the chest) and I could only click yes or cancel, neither button worked. The server was still connected. After a few more moments the UI window closed and I didn't get any rewards and the chest is gone from the warehouse.
I didn't record it, but it happened so I'm not sure if you could code more checks to make sure that doesn't happen without making sure they get the reward.