How can I resheathe behind brick fascia without removing the brick?
"Is there a good and code-compliant way -- and barring that, just a good way -- to rectify this situation WITHOUT REMOVING THE BRICK OR INTERNAL STRUCTURE?"


No.


  "I am planning to remove all of the sheetrock and insulation in the affected rooms, cut the brick ties (most of which are rusted anyway) after supporting the fascia from the exterior, slip housewrap between the studs and the fascia, and then slip a sheet of 4x8 1/2" (or less, I think I saw 1/4") of extruded foam sheathing between the studs and the housewrap. The entire thing will be re-anchored and affixed from the outside using CTP Grip Ties or a similar product. This should provide a watertight, sheathed, and even (insufficiently) thermally broken envelope without having to do any tearout work beyond the sheetrock."


Your plan sounds like it could work, (except for the challenge of slipping 4x8 sheets of anything between studs and your bricks).

As a suggestion, I would use diagonal metal strapping for lateral brace across the studs if you are not using structural sheathing (i.e. foam).

See this article (goto page 2) and below image from finehomebuilding.