Repacking the wheel bearings when the rotors are changed could be as often as 10,000 miles to 100,000 miles depending on driving habits.
I repack mine about every 20,000 miles or maybe sooner sometimes.
I figure my life rides on those little bitty bearings, and I do like to check them.
The cost of new bearings and grease seals is not all that much, and a repack is very simple to do. I have one grease gun with just wheel bearing grease and a bearing packer that pushes the grease through the bearing.
DIY and it just the cost of grease and seals plus your time, plus you can clean and check other stuff the $100.00 per hr shop monkey won`t do.
The closest I ever came to losing a wheel because of a wheel bearing, was back about 1970. we were driving a Ford F-600 truck. the three of went down to watsonville to have breakfast, there was a place to get it for 99¢.
we were hauling butt back to Santa cruz to get back to where we were suppose to be working (about 20 miles), before our forman came out to check on us.
started to smell the odor of hot breaks, so pulled over. the L/F wheel was at the end of the spindle at a 45deg angle ready to fall off.
. never felt anything in the steering to indicate a problem, but I was 25 and an expert back then
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Charlie