AI Mickey Mouse is a possible copyright as well as trademark violation which would likely be enforced in the exact same way if you were to hand draw it. This type of violation is not AI specific.
The main threat that AI poses is not that it outputs copyrighted characters, instead brand new works that are either totally new (idea is never drawn before but the style is derived) or different enough from a known character to be considered a derived work.
Another way to put it: artists' current job is not to draw mickey. It is to draw new works, which is the part AI is threatening to replace. Sure, Disney may chase the AI companies to remove Mickey from the training set, and then we lost AI Mickey. That doesn't solve any problem because there are no artist jobs that draw Mickey.
Even in the case of extreme success where it becomes illegal to train a copyrighted image without explicit consent, the AI problem doesn't go away. They'll just use public domain images. Or sneak in consent without you knowing it. As was the case with your "free and unlimited" Google Photos.
Finally, if there's any player interested in AI art, it has to be Disney. Imagine the insane productivity gains they can make. It's not reasonable to expect that they would fight AI art very hard. Maybe a little, for the optics.
This will closely mimic van Gogh's style but nobody cares because style cannot be copyrighted in itself. So it draws a robot owl, which for the sake of this example, is a new character.
Zero copyright violations.
My point remains that AI users aren't going to aim for output that directly looks like an existing character. These artists are now intentionally doing that for the sake of the protest but this is not how AI is used. It's used to create new works or far-derived works.