Deleting an account is permanent. There is no recovery window, no support request that reverses it, and no backup that can be restored on request.
Two things routinely surprise people, and both are worth understanding before you decide rather than after:
Secret chats are not affected because they were never on our servers to begin with. They stay on the devices that hold them until those devices delete them.
The real flow asks once more after this, in a dialog, because a button labelled with a permanent action is too easy to click by accident. If a cloud password is set on the account, it is required here.
Deletion is queued rather than instant. Messages are removed from our servers immediately; the account itself is held briefly before it is erased for good, and signing back into the app during that window cancels the deletion.
That grace period exists for one reason: people delete accounts in the middle of a bad hour and want them back in the morning. Once the window closes, nothing can be recovered.
Deletion is heavier than most people need. Signing out of a device ends that session. Muting a chat stops the notifications. If the account itself is what you want gone, this is the page — but it is worth being sure that is the actual problem.