After testing it with having killed the boss already for the week, you can infact repeat the boss over and over and get a chance at loot with your bonus rolls.
On Sunday I went to LFR Terrace of Endless Spring and we killed the first boss. I got my gold bag and didn't use a bonus roll. Everyone left the raid before Tsulong, no idea why... but ok!
The raid filled 2 more times and people continued to leave so I decided to do the rest on Monday.
Monday comes around, I kill the first boss for the 2nd time for the week. So of course no loot or gold bag, but the bonus roll popped up!! I was surprised!
So now my question is...!?!/11!! Had I pressed the bonus roll would have I had a chance at loot? Meaning I can use all my elder charms in one week on the same boss if I killed it 10 times if I wanted too? Or is it a guaranteed gold bag or quite simply a destroying of a valuable coin?
TLDR: I was saved to a boss and the bonus roll popped up. Can I potentially use my bonus roll on that boss 10 times for the week if I wanted too?