When a member is removed from a plan all the data that they collected while they were a member of the plan will stay in the plan.
The data/records will still contain their user account information in the "created by" and "updated by" metadata fields.
If record assignment is being used, you will have to reassign the records to another member during the removal process.
If the user has unsynced data on the Fulcrum mobile apps and they are removed, this data will not be synced to the Fulcrum servers. Any sync attempts made by a user account that was removed from a plan will fail.
If the member created any apps, layers, or choice/classification set lists they will also be retained in the plan.