A threat actor is an entity or individual that poses a potential harm or danger to an organization's information systems or data. Terminated staff are the threat actors in this scenario, as they are former employees who may still have active privileged accounts that grant them access to sensitive or critical information or resources of the organization. Terminated staff may abuse their access privileges or credentials to compromise the confidentiality, integrity, or availability of the information systems or data, either intentionally or unintentionally. Unauthorized access is a threat event or action that occurs when an unauthorized entity or individual gains access to an organization's information systems or data without permission or authorization.
Unauthorized access is not a threat actor, but rather a result of a threat actor's activity. Deleted log data is a threat consequence or impact that occurs when log data, which are records of events or activities that occur on an information system or network, are erased or corrupted by a threat actor. Deleted log data can affect the auditability, accountability, and visibility of the information system or network, and prevent detection or investigation of security incidents. Deleted log data is not a threat actor, but rather a result of a threat actor's activity. Hacktivists are threat actors who use hacking techniques to promote a political or social cause or agenda. Hacktivists are not the threat actors in this scenario, as there is no indication that they are involved in this case.

The most important consideration when developing tabletop exercises within a cybersecurity incident response plan is to identify the scope and scenarios that are relevant to current threats faced by the organization, as this will ensure that the exercises are realistic, meaningful, and effective in testing and improving the incident response capabilities12. The scope and scenarios should reflect the organization's risk profile, business objectives, and operational environment, and should cover a variety of potential incidents that could impact the organization's assets, operations, and reputation34.
References
1: Cybersecurity Incident Response Exercise Guidance - ISACA 2: Cybersecurity Tabletop Exercises:
Everything You Ever Wanted to Know 3: CISA Tabletop Exercise Package 4: Boost Your Incident Response Plan with Tabletop Exercises