Bummer! But it happens. If you show fish long enough, or even handle them or transfer them at season's end, you WILL have a fish with a broken fin bone somewhere along the way. And that guy Murphy has a law that says it will happen to your best koi at exactly the wrong time!! The common ones are - the dorsal fin bone, the leading bone on the pecs, the anal fin and the top of the tail/bone. Often it is from getting caught in the net and the fish twists and snaps the entangled bone.
The reason these bones don't heal so well is because the fish uses them so much that they never seem to knit right or at all in some cases. Hobbyists have tried ice pop stick splints, sowed/sutured x-ray film cut out forms to the fin and one I have used- super glued the bone together. All have limited success.
If the bone does heal it often heals with a knock or knuckle where the break was. Or a wave. So the show career is often in jeopardy.
But I have seen some good healings as well. Never completely undetectable but un-noticable upon casual review. A lot depends on the freshness of the injury, the size and age of the koi and the time of the year. You have ALL those things in your favor at the moment so I would not give up. If it was a jumbo female I'd be letting you down easy as this point in the conversation!
what ever you do, put the fish under to work on it and do not try any repair while the fish is awake-- unless you want 'matching' breaks!
JR