When you select 'Delete account files' TB is supposed to really remove them.
You can check whether they're still present by going to your mail directory and checking whether there's still a directory with the same name as your deleted account.

When this fails, ther only thing that could help you is an undelete tool. However, when you have't got one of those installed, the odds are that installing it will diminish the chances you've got for a successful restoration.

Your best option would be falling back on a previously made backup.