Its not about no longer existing. If you take this URL - https://translatewiki.net/wiki/User_talk:ReplaceMe and replace the "ReplaceMe" part with any other string, you will still see the same page. Its a default template that appears for non-existent talk pages, irrespective of whether the user existed before or never existed.
But if there was never a user with that name, as you say, the page should not exist... I change the url to the page that requested the deletion and it still exists. Only admins can delete it.
It is very simple to press the delete button please, if another user comes later and wants to make an account the page will be created again, although it is unlikely...