Personally I would stack the odds in his favor by using the rifle,
Bow is great, but with its limited range, will have lower chances of success.
waiting 8 yrs for another tag is a loong time, especially to a 13 year old.
If 40#'s wasn't enough to comfortably take down a bear , states would have higher poundage restrictions.
Whichever you choose, good luck, will be heck of a memory for him