Can I safely remove obsolete Tracker entries within the Administrator>> Users section? Will historical data in the database be lost? Will it also automatically remove them from any Assignee entries and subgroups if I purge those users?
These obsolete users can be selected and deleted from Administrator>> Security>> Users. You may run into an error that they have open items associated to their login and you may have to close older tickets if open.
Call Ticket information will not be touched by you deleting a Tracker's login. There are no cascading changes anywhere in HEAT.
Assignees from the Assignee table and Assignees on Assignments are completely unrelated to the Tracker Login. If you need that same value removed as an Assignee selection, then you will need to remove that value from the Accessory>> Table Maintenance>> Assignee table.
Attached is a SQL Stored Procedure and query that can be run to find a specific value throughout the entire DB. This may be helpful in locating all instances of a specific login name that needs to be either deleted or changed to another value.