Legal Question in Landlord & Tenant Law in California

That depends entirely upon what the lease terms say. If, as I suspect it does, state the the unit is rented to both of them, then they both must leave for the lease to end. Your brother signed a contract to have the legal right to occupy the unit, not to pay based upon how often he actually is their. If his roommate remains, he will still have access to the unit. It is similar to a person who co-signs a loan on a car; they have to pay no matter what happens to the car. Your brother might have the right to sue his roommate for whatever your brother pays, but does hte roommate have enough money and other assets so that he could collect against him?

Mr. Shers is right on this one. Your brother and his roommate are jointly and severally liable to the landlord for anything to do with the lease. Your brother has a right to indemnification from the roommate for anything he has to pay for that is the roommate's fault, but if the roommate doesn't have any money, that will do no good, and in any case it will look bad on credit reports, etc. Your brother needs to work this out for the roommate to get another roommate and sign a new lease, or move out when the lease ends.