I have asked a question. A user left a comment which addresses my problem (a confirmed bug with a specific version of a software). I wish to thank the user with a comment and delete the post now that it is no longer useful or meaningful. Can the user still receive my comment after I have deleted the post? Or should I wait for the user to log on again before deleting?
The user will not be able to see the comment once your post is deleted, unless the user has more than 10k reputation.
I believe that even for 10k+ users the comment would be removed from their inbox; they would have to explicitly look up your post (for questions that means they need to know the exact URL).
Generally, if I am going to delete a post but want to leave a comment I want someone to see, I wait a day or so, and include something along the lines of "I'll delete this post in a day or so". You still cannot be certain anyone will have seen your comment; you could monitor their 'seen' value on their profile but that's not a guarantee they actually read their responses.