In many cases, a user does not want to deactivate his account for a while to restore it later, but for some cases, he/she wants to quickly delete the created account with its domain and is sure of its deletion. Please create such an option.
Never delete an account with the domain still on it, as that domain will remain locked on the hosting system forever. The client area should display a warning about this; always make sure you have removed all domains from a hosting account before deactivating it.
Then just reactivate the account, delete the domains from the account, and then deactivate the account again.
You cannot delete accounts immediately, but you also don’t ever need to do so, because whether your domains are locked to your account is entirely up to you.