[PAULUS libro secundo quaestionum. ] §5.1.46.prIudex datus in eodem officio permanet, licet furere coeperit, quia recte ab initio iudex addictus est: sed iudicandi necessitatem morbus sonticus remittit.
[PAULUS, Questions, Book II.] A judge who has been appointed remains in the same office, even though he should begin to be insane, because he was legally designated as judge from the beginning; but a serious illness excuses him from the necessity of judging.
ergo mutari debet.
Therefore, he must be replaced.