They are already here.
Anyone that thinks the there is a chance that ATF will be defended is just stupid. Republicans or Dems, doesn't matter. The ATF isn't going anywhere.
Yeah, not without legislative action to remove the provisions of the National Firearms Act, the Gun Control Act and other related laws. ATF derives its power (and continued existence) from those pieces of legislation, so without repeal of the pertinent language, enforcement would just be shuffled to some other federal agency. Possible? Yes... but the probability is vanishingly small.