When a jury becomes unavailable before a verdict is returned, the result is a mistrial. Likewise, when a judge becomes unavailable before the statement of decision is entered, the result is a mistrial. Both common law and statute entitle either party after trial to ask the trial judge to decide the cause independently as the "thirteenth juror." So it stands to reason that, if the judge becomes unavailable before a new trial motion can be decided, the result should be the same: mistrial.
But that is not the way the cases have come out where the trial judge becomes unavailable before deciding a new trial motion. As illustration is the recent case of Hakenjos Hall Prof. Svcs, Inc. v. Korte/Schwartz, Inc. (D4d1 Jun. 17, 2021) 2021 WL 2461132 (nonpub. opn.). After a jury trial by experts over business damages, the trial judge retired, and the defendant moved for new trial. A new judge denied the motion, and the Court of Appeal held that substantial evidence supported the verdict.
I offer some reasons why this may give short shrift to the standard on a motion for new trial.