Regardless, the human generating and publishing these images is obviously responsible to ensure they are not violating any IP property. So they might get sued by Disney. I don't get why the AI companies would be effected in any way. Disney is not suing Blender if I render an image of Mickey Mouse with it.
Though I am sure that artists might find an likely ally in Disney against the "AI"'s when they tell them about their idea of making art-styles copyright-able Being able to monopolize art styles would be indeed a dream come true for those huge corporations.
So in effect, they are pitting Disney's understanding of copyright (maximally strict) against that of the AI companies (maximally loose).
Even if it's technically the responsibility of the user not to publish generated images that contain copyrighted content, I can't imagine that Disney is very happy with a situation where everyone can download Stable Diffusion and generate their own arbitrary artwork of Disney characters in a few minutes.
So that strategy might actually work. I wish them good luck and will restock my popcorn reserves just in case :)
The problem I see though is that both sides are billion dollar companies - and there is probably a lot of interest in AI tech within Disney themselves. So it might just as well happen that both sides find some kind of agreement that's beneficial for both of them and leaves the artists holding the bag.
There are noninfringing usecases for generating images containing Mickey Mouse - not least, Disney themselves produce thousands of images containing the mouse's likeness every year; but also parody usecases exist.
But even if you are just using SD to generate images, if we want to make sure to avoid treading on Disney's toes, the AI would need to know what Mickey Mouse looks like in order to avoid infringing trademark, too. You can feed it negative weights already if you want to get 'cartoon mouse' but not have it look like Mickey.
The AI draws what you tell it to draw. You get to choose whether or not to publish the result (the AI doesn't automatically share its results with the world). You have the ultimate liability and credit for any images so produced.