CA Prob Code Section 8521

(a)

Unless the will provides otherwise or the court in its discretion orders otherwise, if a vacancy occurs in the office of fewer than all personal representatives, the remaining personal representatives shall complete the administration of the estate.

(b)

The court, on the filing of a petition alleging that a vacancy has occurred in the office of fewer than all personal representatives, may order the clerk to issue appropriate amended letters to the remaining personal representatives.