The reasonable answer is also a political fork.

The author is entitled to use whatever license they want, and the community is entitled to a fork if it doesn't violate the previous license. That's all there is to it. the author doesn't owe the community anything, and the community, as long as they respect the terms of the previous license, is free to fork the project and get rid of the new license.

In general, these political stunts eventually reflect badly on their author. Open source is a double edged sword.