I can't find any help regarding this… in Zoho CRM a Contact has just quit his job. We don't know where he'll work next, but obviously, he's no longer part of the company listed in Accounts

If we delete him, then we lose all of the history attached to him (and the Account). 

Is there a way to "retire" him or suspend him?  What do you all do when a contact/lead quits their job?

It's likely that in a couple of months he'll surface again working at a new company- at that time, should be treat him as a brand new contact and enter him with fresh details, or just modify the company name/address/tel details in his existing contact record?

I look forward to hearing from you.