I have been in the health insurance industry for 20+ years, as a Case Manager, Regional Service Manager and expert witness for the courts. I am also in California. ALawyer is right about most policies terminating at the end of the month; however, some employers do have policies whereby the coverage will terminate the day employment ends. This type of temination provision is typically seen at larger companies that employ over 100 people. Since you mentioned that your employer has multi-locations, this very well might be the case with your policy. If you look in the policy booklet you got from your insurance company it will tell you exactly when your coverage terminates. Or you can call the insurer's customer service department and ask them when your coverage terminates. They will have that information readily available to you in their computer.
As far as your payroll deduction goes, if your coverage terminates the last day of your employment, your employer MUST REFUND ANY AMOUNT DEDUCTED FROM YOUR PAYCHECK FOR COVERAGE YOU WILL NOT BE ELIGIBLE FOR. You should not only report the employer to the DOL, you should call your insurance company and tell them also. They will address the problem with your employer, as it puts them in a possible position of risk... to say nothing of the risk your employer is assuming for himself. By not refunding the payroll deduction to the employee, it puts your employer "on the risk" (responsible) for any claims that might be incurred by the employee during the period of time that payroll deduction covers. In the event a claim does occur, the employer would find himself in a position whereby he would have to fund for the claim; and, the employer would have to provide the same benefits that the group policy offers, OUT OF HIS OWN POCKET. I have seen this happen to employers, and when it does, it's usually because the employee has had an accident, and the resulting financial loss incurred by the employer is usually devastating.