Those pieces are from the ball retainer, I originally thought you meant the outer ring of the bearing came apart.
I have seen a lot of ball retainers fail over the years. I never saw or heard of it in one of our bikes, but I have seen it on a lot of bearings in other applications. The 2 halves of the retainer are usually spot welded together in between each set of balls, it only takes one weak weld to start the failure in progress. Once one weld fails the next ones are under a much higher load and also soon fail, once it starts it all happens pretty quick.
I don't know if it can be done, but it almost looks like you could get that bearing out, and a new one in, without pulling the engine or splitting the case. Even if you can get the bearing out, you would need to put the jigsaw puzzle of bearing pieces back together to be sure that all of the parts are accounted for, any one piece that would be left in the transmission and found its way in between 2 gears would be a very bad thing.