- Who provides the notification (might be HR, might be the manager to whom the employee reports,...)
- Disabling logins
- Archiving emails, home directories, project repositories
- Establishing exit interviews
- Defining last-minute deliverables (typically just knowledge transfer)
It's worth pointing out that you can't know that this isn't a "disgruntled employee scenario" unless you have learned to read minds. They wouldn't be leaving if they were 100% happy.