The end of a relationship.
FIRST, ASK WHY
Genuinely. Sometimes it is a fixable problem nobody told you about.
Sometimes it is price, and sometimes their business changed.
IF IT IS FIXABLE
Offer to fix it. A client leaving over a problem you did not know about is a preventable loss.
IF IT IS NOT
Accept it gracefully. Arguing achieves nothing and they will describe how it was handled.
WHAT TO PROVIDE
A full backup of their site and database Their email, or instructions for downloading it DNS records Domain transfer, if you hold the registration Help with the migration, if they want it
Promptly and without obstruction.
WHY BE HELPFUL
Your reputation in a small market. A client who left smoothly speaks well of you; one who was obstructed speaks badly, at length.
Some return.
WHAT NOT TO DO
Withhold backups Delay a domain transfer Delete the account before they have what they need
TIMING
Give them a stated period to collect everything before terminating.
WHAT TO LEARN
If several clients leave for the same reason, that is the reason to address.