Possibly.
It my assumption (but I may be wrong and your right) that as long as the UFC can maintain that their their belt is just a prop used for promotional purposes and not an actual signifier of who is the best in the world (which is what the UFC has argued in court). Fighting for that belt would never be mandatory.
Possible, but I strongly doubt it. The UFC has built too much brand awareness. As long as the UFC is able to hand out their fancy "trophies" they will still be considered the most valuable title among the general audience.
While the Championship Clause might, and that's a big maybe (I remain skeptical), get tossed out.
The overwhelming majority of UFC contracts would still be upheld under the Ali Act.
And they would still be the highest paying organization in MMA. OneFC and Bellator wouldn't magically gain the monetary resources to outbid the the UFC. They maybe be able to get a star here or there, but both of those companies would still be operating in the red whereas the UFC has over a billion dollars in contracted revenue coming in each year.
The market forces at play that dictate pay wouldn't change. A union is the best case scenario for everyone involved.