With thanks to Gail Moss, a long time fan of MTW, who posted this info on our Facebook page in late 2022:
"I called on November 8, 2022, and spoke with an employee. This is his current information."

Cornerstone Talent Agency
Michael T. Weiss
37 West 20th Street, Suite 1007
New York, NY 10011-3714
USA

Phone: (212) 807-8344
Fax: (212) 807-8662

At least, my birthday letter 2023 still wasn't returned eight months later.
Mike's definitely gone off the grid. I hope he is living a life that makes him happy. That's the best we can hope for.