[UPDATE: It turns out that at least some cases suggest that, if a mark is found not to be protectable — including because it’s disparaging — then the owner of the mark cannot use federal trademark law to prevent unauthorized use of the mark by others. See In re Tam (Moore, J.), pp. 7-8 ; the cases cited in that opinion for this proposition don’t squarely discuss marks that are unregistrable because they are disparaging, but the cases can indeed be read as denying all federal protection for such marks, and not just the special protection offered by statutory registration.

On the other hand, the PTO document I cited above pretty strongly suggests that some federal protection would indeed be available despite the cancellation: “Losing the federal registration of a trademark does not necessarily mean that the owner loses all legal rights in the mark. This is because trademark rights in the United States come from use of a mark on or in conjunction with goods or services, not merely from the additional, optional step of federal registration.” And in any event, the loss of registration does not prevent the owner of the mark from using the mark, or (I think) from filing lawsuits under state unfair competition statutes for unauthorized use of the mark, even if it prevents federal lawsuits based on unauthorized use (and thus sharply diminishes the value of the mark).]