As far as I know every boss does that with the exception of warzone 4, 5, and 6 but seems like it was secretly fixed because even if you die you get rewards if you hit it. Even if you're killing a boss that has conflict with others monsters and still die you get rewards. For example, the other day I was doing Drume and it summoned one of the most damage dealing falcon mini boss and it killed the 3 lion commander and made me leave while Drume was in dark red which was close to Kesar,. I left because I failed and went to scarlet. When I was at Ankrahmun desert a message appeared about the loot I got from Drume. So even if a monster in conflict kills the boss while you are out of the arena and you did certain damage you still get rewarded