I would rather answer that it depends on boss' reward system.
Generally it is possible in case of all bosses with reward chest system, based on participation. The value of a loot depends on how big participation you have made, so when you die at the beggining of the fight, it is possible, that you will loot only some gold coins or rubbish, but when you die in the end, death might increase your participation and help you win the loot. All you need to remember is to stay online after the fight.
Here is my old screenshot - I died when Prince Drazzak was on black HP. My team luckily killed it few seconds later:
The same situation looks differently when boss has no reward chest system and the loot win player with the highest damage. Yes, in this case you will also win the loot if you are the one, who made the biggest damage, but it is rather impossible to get your reward, if you die during fight with the boss. If you stay online, you will see information about the loot, but you will have only 10 seconds to open the corpse. So in fact it is too short time, to come back and take the loot. After 10 seconds everybody will be able to open the corpse.