I did a little digging myself, and found that the
FAQ has the answer. Scroll down to [Battle 13] (about halfway down the page), last paragraph:
Result of Victory: Ryvern runs away (again), and Whirlwind opens the way to the next area. If you decide to return Whirlwind will challenge you again, only this time Leo will join in the fun. If you win this rematch you'll get the Extra Sanctum Guard card!
Good luck!