I have a 1992 toyota 4x4 x-cab. The outer flange dust cover has rusted away, the rest of the backing plate is in good condition. How important is this outer dust cover flange. I do not do any off roading just snow duing the winter.

This dust cover is pretty much unimportant. I actually had to remove one of the dust covers on my wife's 1990 Toyota Camry when it rusted to the point where it bent and touched the brake rotor while driving, making a horrible noise. We noticed no ill effects from doing this and we never replaced the dust cover. You should be fine to remove the sharp edges or remnants of the dust cover and keep on rolling.