If it's truly accidental (as in a rogue employee or a script that f'd up), they probably have a legal basis to break the contract/license terms and retract it. Just as stores are not required to honor misprinted price tags. There will likely be a court case if someone believes they legitimately received a GPL-licensed version of the code and wants to use that code in another project (or pass it on to others). Like I said, I think Adobe has a good case to win that here.

If it's "accidental", and they're just trying to walk it back, there would definitely be a court case. Whether they'd win or lose would be very up in the air, and probably depend on the jurisdiction's friendliness to businesses.

Without accepting the GPL, use of GPL code is generally a copyright violation, but it can be litigated as software piracy, which may have various outcomes based on how serious that is.

They could choose not to continue to distribute the code though (but good luck clawing back the GPL licenced copies).