Only if your license is covered under copyright. Contracts are functional instruments, so copyright doesn't always apply. You, as a license author, may in fact be required to demonstrate to a court that your license is not only original and creative enough to be valid copyright, otherwise they're going to throw out the case.

And even if you do manage that... it doesn't change the obligations, right and conditions of the license people agreed to. After all, they agreed to a contract, irregardless of that contract being in copyright violation. So even if a license author sues, they can't help people already under that license. And the most likely court outcome is that the software under license becomes proprietary once the court decides you can't use that license text anymore.