Trevor the Guru here!
When an account is fully closed down this transitions the account off billing for any Shopify related charges. This includes any app charges, subscription charges, and any other charges that would have appeared on your monthly invoice.
Domains are a bit of a difference however as domains are set up on yearly bases and not a monthly base. If the domain was set up to auto-renew then there is a chance you will be billed again when it comes up for renewal. If we're unable to process the charge for the domain then it will eventually go back into the public register to be purchased by someone else.
If there are any other questions please feel free to reply back, or phone/chat in! We are here 24/7! :)