Well I have experience with that. LOL
My SA XL-FDD dyno hub, with 17,000 miles, ATE 4 bearing in a sealed unit. This hub took a some hits on a tour 7 months before and I went for a 90 mile ride on the highway just a couple days before I noticed something wrong. It was feeling strange leaning in a curve and had an intermittent side to side looseness when I was stopped and trying to wiggle it. I was then riding slowly on a 12 mile ride when I finally decided it was seriously bad. But I still rode it home slowly keeping it straight up.
So the next day I took it apart. The crumbs were all stuck on the magnet, 4 of the 11 balls were gone. LOL Everything else had NO lube whatsoever and had no discernable pits or marks.
So I got out the vacuum cleaner to help suck the chips off. I then couldn't find any other scratches or damage. So I went to the industrial bearing warehouse and got some new sealed bearings. I had to unsolder the wire to get it apart. I didn't need a keeper for the magnet that I could tell., still powers fine. Oh, but first I had to make a 33.5 mm hexagon tool with 1/8" a steel plate, to open the soft Alu shell. This hub just did another tour, now 24,000 miles. Sturmey Archer stuff is TOUGH. ha I'm not sure how the hell 4 balls could make all those little bits.