There's no method in place to allow for direct contact over the forums. I'm not sure what the long term plan for the forums is, but I personally hope no such internal messaging / email is ever added.
Now if the forum reply is gone it would be (likely) down the forum bot that cleans up spam, or spammy users. Sometimes it is a little too heavy handed and removes things it shouldn't. It would be up to that user to reach out to support to have it returned.