More realistically, California stops growing alfalfa and stops raising beef cattle altogether. That would free up enough water to water every lawn across the state.
I was just looking into a fake lawn for my next house, but you don't recoup the cost for 7 years. The builder has been putting in smaller lawns in the front, so we'll likely put a small one back and be smart about watering it (not in the middle of the day, properly position sprinklers etc.). Or we'll xeriscape it
http://scienceline.org/2011/07/lawns-vs-crops-in-the-contine...