I would say that CtR cards would then become CBN, since if you can't undo the withdraw they would be useless to negate as that would have one of results, either the whole thing becomes CBN, or you can negate the choose but not the withdraw leaving you with no character in battle and thus their win. Apparently CtB/R has a withdraw component (according to the rules) in the same manner that exchange has a search component.
