If there is any way to undo the unlearning, there is also a way to use that method to identify the weights carrying the information to stop them from conveying

If there is any way to undo the unlearning, there is also a way to use that method to identify the weights carrying the information to stop them from conveying that information. At the heart of training is detection. The information may still be in there, but undetectable by any known means. You can definitely certainly remove the information, setting every weight in the model to zero will do that. Identifying when you have achieved the goal of completely removing information while not destroying other information might not be possible. I'm not sure if that will mean there might in the future be something analogous to zero-day unlearning reversal exploits.