Normally an ABS failure won't affect the brakes unless you have the old Bendix system 10 (Chrysler used it in the early 90's, I don't know what system GM used at that time). Maybe try your recall search without ABS in the search text. Is there any chance the engine could have stalled or tried to stall and maybe sputtered a bit and started running again? A stall could give the same symptoms as the vacuum pressure for the power brakes went away (most people have never driven a vehicle without power brakes and will confuse loss of power brakes for a complete loss of brakes, though your pumping should have done something)