43 CFR 45.32: What happens if the ALJ becomes unavailable?

(a) If the ALJ becomes unavailable or otherwise unable to perform the duties described in § 45.31, the Hearings Division will designate a successor.

(b) If a hearing has commenced and the ALJ cannot proceed with it, a successor ALJ may do so. At the request of a party, the successor ALJ may recall any witness whose testimony is material and disputed, and who is available to testify again without undue burden. The successor ALJ may, within his or her discretion, recall any other witness.