I actually had the reroll count on that full blog post:
http://blog.askmrrobot.com/2016/07/o...the-bones-rtb/ For a 450 second average fight length.
If you never reroll, you apply Roll the Bones 11 times in a fight. If you reroll for shark or any-3, you use it 30 times. So on average, you are rerolling twice (for a total of 3 rolls) to get either any shark combo, or any 3 buff combo.
But as people already pointed out, you don't know how many it will take when you start rolling. It could take 10 on one try, 1 on another. So it isn't helpful in the decision making process. But the simulator does this over thousands and thousands of iterations, giving you the average, and accounting for the DPS loss by not casting something else.