Dietreich Blackstone likely would have faced more pressure from his family to join the Fists of Rhalgr and might have actually made a decent brawler. Had things gone differently, he might have even become an actual monk. His dedication to the art might not have been so great as his brothers, and of course the King of Ruin had other plans for the temple anyway. Chakra or no, one could still find plenty to fight.
He and his family probably would have eventually fled Ala Mhigo, perhaps to settle in with the Resistance in the Shroud. Little Ala Mhigo was a coward's den as far as father was concerned, and his sons would have no part of it, either. So they would put up with the snivelling fools who look down at them in the name of their elementals and work to piece together something to keep them afloat until the day they could return home. Dietreich might have taken up the lance, even, between whatever other jobs he could find: the fist was a true Ala Mhigan art, of course, but there was something just so satisfying about sticking someone with a polearm. And if that someone just happened to be a Garlean, well, that just made it all the better! Hunting Imperials was sure to be a quick way to earn coin and reputation. Maybe someday he'd get it in his head to call himself Grimsong, just so they'd know to be afraid if they ever hear him coming.