The B-1B wasn't in service yet in 1982 in the USAF, but ignoring that....
Much would depend on what they are armed with. Just using Shrike anti-radar missiles and dumb bombs are OTL doesn't change the outcome of the raids that much, just a lot more explosions from bomb hits on the airfields. The Black Buck raids didn't do all that much damage, but if the RAF bombers are equipped with penetrating bombs or thermobaric weapons that could change dramatically.
Attacking the Argentine mainland could have been done by the Vulcans, but they chose not to, even though it could have been useful. The B-1 would be much the same, if anything hitting any Argentine bases aside from the ones in Patagonia would be easier than the Falklands due to lower distances, but stronger fighter protection could be a problem.