The CA version of WARN known as "RMLT" does not address how mergers and acquisitions are handled.
However, under RMLT, you are a covered employer under if you have more than 75 employees and are laying off 50 or more employees. Therefore, you may not have to worry about the RMLT, nor the Federal WARN Act.
I would strongly advise getting a legal opinion from a CA employment attorney before proceeding.