Max hours a day working

Hi guys, 

wanted to get your advice. I work as an RN in LTC in CA, 12 hour shifts. We recently went through a huge staff quitting spree, including the DON and management team leaving. Now we have to heavily rely on registry RN nurses. They are great, but sometimes they don’t show up or cancel. It looks like in CA, mandatory overtime is not allowed, but I am extremely nervous about leaving without giving report to an RN. I have talked to upper executive management that if this ever occurs, I want some kind of letter stating that I gave notice that I cannot stay beyond my shift and they are aware there is no RN for the next shift. I am concerned about my license or having to work 24 hours straight.