I have a staff member that has unceremoniously left work, is it possible to get access to his files/chat groups etc he has created?
Files I can get from the server, however I am not able to see any chat groups he has created and he is the only admin for them. I would like to add more to the talk groups etc.
You can use the app Impersonate to change from an admin account to another user.
Basically, your approach is a major intrusion into data privacy. I would clarify the procedure in advance and only carry it out in a four-eyes-principle. With another person together Install app Impersonate, change to user, view and copy information, log out the user, uninstall app Impersonate. Make a protocoll of all actions and signs it both.
Normally if a user is gone all files and chats have to be deleted. Something like this is quickly a data protection violation. Is it really that important? If not, then let it be.