The mandate of an arbitrator terminates if he becomes de jure or de facto unable to perform his or her functions or for other reasons fails to act without undue delay, and he withdraws from his or her office or the parties agree to the termination of his or her mandate.
Source:
Section 1297.141, https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=CCP§ionNum=1297.141..