Organisational debriefs vary in scope.
Where your are reviewing the management of an event, an incident - or indeed, a complex circumstance which put the organisation under significant stress the specific matters under consideration will vary - but the methodology of 'debriefing' need not vary. Hence the use of a structured methodology.

The tools appropriate to achieve the objectives are highlighted with the green dots in table above.
This can generally be done working remotely with your nominated representatives by email and phone - with a webinar seminar by video link to follow up on the initial work with your team. The option to conduct the seminar face-to-face can always be considered as a variation if required.
As the incident under review becomes more complex - involving other stakeholders; and in some cases significant personal and political sensitivities, it is beneficial to use face-to-face contact for the seminar.

The most effective way of meeting your needs starts with a conversation focused on scope.