Disabling old End Users vs. Deleting old End Users

I attempted to find best practices or similar questions in the forums and documentation but couldn't immediately find it.

We have a large amount of end users for a "Domain" "Company" (whatever you want to call it) that we no longer provide service to.

Those end users originally we brought in via LDAP integration.

Disabling them all seems like something I should do ... right?
Deleting them seems like it will break their ticket history?

I'm pretty new to SysAid Administration, and I don't have a colleague who knows more about SysAid to lean on.

Not asking you to solve my problem for me, Just point me to the right Best Practices Documentation for this kind of situation, or the risks, rewards, for disabling/deleting these end users.