>If Patrick S Ditko is successful against Marvel in terminating copyright, this does not mean that Marvel Comics would have to stop publishing Spider-Man or Doctor Strange; they would still own the trademark for both. But elements from the two comics cited here could not be used in current comics and films.
This is false. If copyright is terminated, it doesn't mean Marvel can't use those elements anymore, it means anyone can use them now. It means anyone could use elements from Amazing Fantasy #15, for example, so you could use Spider-Man and Uncle Ben in a story, but not J. Jonah Jameson, because he was introduced a few months later in Amazing Spider-Man #1. But when the copyright on that expires, then you could use Jameson, and the Chameleon and a few other characters, but you couldn't use elements that were introduced later even as related to those characters, so you couldn't say The Chameleon is Kraven's brother, even once Kraven becomes public domain, because the story that said they were brothers was much later.
If Disney has a trademark on Mickey and not a copyright, you can still use Mickey, you just can't use him in advertising. You could make a work with Mickey in it, but you probably couldn't use the words "Mickey Mouse" in the title, or feature him on the poster, unless you change his appearance significantly.
A good example is Captain Marvel. Fawcett Comics made a character called Captain Marvel in the early '40s, then went out of business (thanks to DC winning a case that said he was a copyright infringing copy of Superman). Decades later, DC started making Captain Marvel comics, but Marvel had already taken the trademark, which had lapsed since Fawcett nor anyone else was making Captain Marvel products anymore. Marvel had been using that trademark to sell products with a completely separate character also called Captain Marvel. So DC could use the original Captain Marvel, and since he didn't look like Marvel's Captain Marvel, they could use his likeness on the cover and in advertising (the cover being considered a form of advertising), but they couldn't use the words "Captain Marvel" in advertising. They could use it in the actual work, but not in advertising. So Captain Marvel continued to appear in the books, and in a live-action tv show, and in later cartoons, but his comics/tv shows had to be called "Shazam!" because they couldn't call them Captain Marvel. The character could be, but not the product. In order to ensure they kept the trademark, Marvel had to keep selling a certain number of products called "Captain Marvel" every year. They had to keep using the trademark. Even though their Captain Marvel series were never particularly successful. So if you read Marvel's Captain Marvel series, he basically begins as a Buzz Lightyear style spaceman, then they retool him with a series of wildly different costumes and sets of powers a bunch of times, because they couldn't just cancel the series, they had to keep publishing it in some form, so they just kept trying to reboot it. Until the present day, where he is an awful villainous woman. That's the reason they keep publishing these comics that everyone hates. Of course, there's no legal reason he has to be an awful villainous woman, that's just because of SJWs.
Decades later, in 2012, DC would decide it would be easier if they just changed the name of their Captain Marvel to Shazam, since that was already the name of all of his series. Of course, fans of the series and character disagreed about this being simpler, since changing what you call a character after 70 years is hard, and also it should mean that he isn't able to say his own name, since "Shazam" is the magic word that transforms him (and this inconvenience is actually a plot point for "Captain Marvel Junior," whose magic word is "Captain Marvel") but DC did it anyway and that's why in the recent movie, the character is just called Shazam. But they technically could still call the character Captain Marvel if they wanted to. They just couldn't call the movie Captain Marvel.