Pull the front pump apart and look at the mating surfaces to see if there is any wear.
The cogs should be able to fall out a bit more like in this picture (722.1 front pump)
...and you can go further but I don't have any more pictures of it totally in bits to hand...
(Don't forget to line the holes in the pump with the casting when you get to that stage =>
http://www.peachparts.com/shopforum/diesel-discussion/304903-722-118-automatic-transmission-rebuild-monster-diy-3.html - but that's for later on)
Post up pictures of any wear if you are unsure - I might be able to say if there is a problem or not.
Good news about the bearing @ Ganzeboom
But like you say why did it fail in the first place? It could just be bad luck - I don't know much about the 722.3 yet as I still haven't gotten around to pulling that transmission apart yet - all I can ask is =>
How does the end of the input shaft feel? It will probably be loose now that the front pump is out - but can you see any problems with it?
If you are feeling brave I'd pull the valve body out (not take it to bits - just remove) and see if you can see anything that doesn't look quite right.
I think the 722.3 is supported (like the 722.1) at three bearing points - one at the front just in front of the gearset; one at the back of the gearset; and one in the tail cone. Any serious wear in these three "gearset support bearings" should be evident.