In Campbell-Ewald Co. v. Gomez, ___ S.Ct. ___ (2016), the U.S. Supreme Court held that the defendant may not "pick off" the class representative by offering full individual relief under Rule 68. If the plaintiff rejects the offer, the case is not moot. Slip op. at 6-8.
In California, this rule was established more than forty years ago. See La Sala v. American Sav. & Loan Assn., 5 Cal.3d 864 (1971). The Ninth Circuit reached the same conclusion back in 2011, and reiterated it in 2013, after Genesis Healthcare. See Diaz v. First American Home Buyers Protection Corp., 732 F.3d 948 (9th Cir. 2013) (discussed here); Pitts v. Terrible Herbst, Inc., 653 F.3d 1081 (9th Cir. 2011) (discussed here).