It is less of a tribunal worthy issue, and more of a game mechanics issue.
Intent is hard to prove.
This person might believe in their mind that they are fighting their hardest by not giving in to their opposition. That said, they grief the entire group for an hour plus sailing around when the battle has already been lost.
Or they were purposely griefing for the tears. Who knows?
Hence, a game mechanic to remove such options is likely warranted. Either a quickly shrinking out of zone circle with each kill, and/or passage of time. This keeps them in closer quarters. Or a time out option, where the battle is ended automatically after no damage dealt for "x" amount of time.
Mayhap not the best options, but you get the idea.