They probably realized after you deleted your tag that they couldn't edit theirs. Once a comment has been replied to, it is uneditable even if all replies to it are deleted.
So when they were like "oops, nevermind!" and you said you would have to rewrite your tag, they were probably embarrassed and decided to ghost.
If you want to, just tag them back with something new, or ask if they still have the notification so you can copy+paste.
Re: GENERAL DWRP QUESTIONS
They probably realized after you deleted your tag that they couldn't edit theirs. Once a comment has been replied to, it is uneditable even if all replies to it are deleted.
So when they were like "oops, nevermind!" and you said you would have to rewrite your tag, they were probably embarrassed and decided to ghost.
If you want to, just tag them back with something new, or ask if they still have the notification so you can copy+paste.