I think it is more of a 'it never comes up and there's no evidence that supports their existence'. At least as far as them being affected by the radiation like other creatures did. There's also no normal evidence like cobwebs and such that would signify that they are still around, just normal like they were before. (Except for it seems in one of the DLCs [Brotherhood of Steel] there are cobwebs, but I think that may have been an oversight?)