1996 Chevy Silverado rear end shims

Drive Train Axles Bearings problem
1996 Chevy Silverado V8 Four Wheel Drive Automatic

My husband just replaced the bearings in the rear differential, but did not replace the shims. He drove it and it makes a noise when he turns to the right( it has now been parked since), how bad could this have damaged the rear end when he drove it without replacing them? We have heard that if he drove it slow it would be fine, and other people said if he drives at all it could tear up the gears.