If this user has Skype for Business, they'll need to reschedule any Skype for Business meetings they organized and tell external ...

If this user has Skype for Business, they'll need to reschedule any Skype for Business meetings they organized and tell external contacts to update the contact information for them.

This user will also need to update their user name in any apps they use, like Outlook, OneDrive, and any mobile apps.

Make sure you tell the user about these changes.