Removing license from user, what gets removed and how quickly (returing staff member)

If you think someone will return, you should put their account on hold before you remove the license. As long as the hold remains in place, the data will stay inside Office 365 as the workloads do not remove information when a hold exists. The Exchange mailbox will be an "inactive mailbox" during this time. This approach is often used by companies to keep information for extended periods while they figure out a) if they need any of the data owned by a "leaver" account or b) if someone should take over the old resources.

TR