IAF ID3 allows, in extraordinary events or circumstances like this, postponement of the assessment / audits.
Moreover, according to IAF MD17:2015 Witnessing Activities for the Accreditation of Management System Certification Bodies and/or relevant timeline modified accordingly, it is justifiable and understandable in this situation that a CB or its client refuses a witness assessment by the AB. It is important to make audits only when there is agreement of all the parties involved (client, CB and AB). See MD17, 2.2.2 and 2.4.2. It is also possible to perform partial witnessing (2.4.10).