Google has updated its account retention policy. Canceled Google Ads accounts may now be permanently deleted six months after cancellation. A 30-day email warning will be sent before the account is deleted.
Canceled accounts were previously retained and could be reactivated at any time. Now, they are eligible for permanent deletion. Google is beginning a cleanup of inactive accounts under this new update. Reactivating an account within six months will stop it from being deleted.

This update is important for advertisers who may want to keep historical data or preserve account structure for future use.
Read the official help page spotted by Hana Kobzová here: About Google Ads account deletion.