The current status of a company has no affect on the status of a copyright. Copyrights last for set periods of time and are not nullified by a company going out of business. That's a bad assumption to make.
You're also confusing Trademarks and Copyrights when you state "the characters are most likely still trademarked, but the work themselves should be PD". That isn't the case at all, since Trademarks only protect brandnames and designs (such as logos or specific costume elements for superheroes). Also, Consolidated and McKay didn't own the licensed characters to begin with, so the copyright for the stories in question would not be owned by them but by the companies that created those stories and characters (King Features, for example). To renew their copyrights, all any company that licensed material to other publishers would have to do is renew the copyrights for the individual stories ... they wouldn't need to renew the copyright on the entire publication if they chose not to or if they were unable to due to the comic containing material owned by other companies.
Case in Point: Hasbro owns the characters of GI Joe, as well as holding the copyrights on the comics produced by Marvel Comics, Devil's Due, etc. Check any issue of the Marvel run on that book and you'll see everything is copyright Hasbro Industries Inc and not Marvel. The only thing Marvel owns from that book is "all other material", which would include advertising for their own books. Marvel Comics cannot reprint those stories any time they want to without first working-out an arrangement with Hasbro. However, Hasbro can have the comics reprinted whenever they want and not owe Marvel any money, since they are the original copyright owners to that material.
Regarding the IW books: whether the material was properly licensed or no, Illegal material is not Public Domain, it's simply Illegal. The status of the copyrights on the reprinted material is not affected by what IW did with it but on what the original owners have done or not done regarding those copyrights. Plus, even if the original material is Public Domain, the IW books may not be if the copyrights to those books have been renewed.
I would prefer not to see this site get shutdown because of a false assumption regarding the legality of illegal reprints. Let's err on the side of caution and "Just Say NO to IW Publications".