If you didn't have the bonus roll when you killed him can you go back and kill him again to use a bonus roll? My guild only does normal so I think it would be worth it.
I'm a bit confused by the new world bosses, I am sure I read that each week 8 out of 11 would be active, and kill able when WQ is up.
only seen one up this week, Nithogg in stormheim
From Wowhead:
"With Legion comes 11 new World Bosses who are associated with epic world quests. They will be available when their world quest appears on your map, and these quests last several days. In addition to their loot, you will receive the reward from the world quest, which can vary from week to week and include Order Resources, gold, and Artifact Power items."
So a new world boss will probably be up Friday/Saturday time frame.
"Clearly every aspect of one's life, from financial stability to social popularity, to sexual prowess can be boiled down to 4 numbers: One's Arena rating" ~ Xandamere