I posted a comment, which was replied to, but I do not see the comment anymore.
Yep, it was me.
I've undeleted it, but... there wasn't really any context around the comment. Helpful may not be the standard for comments, but constructive is. What was the user meant to do, based on that comment?
I don't really believe that a user's reputation should have bearing on whether they may post unconstructive comments or not. If a user's reputation was supposed to be a factor in how valuable a comment should be considered, it'd probably be visible at all times on the comment, and not just in the tooltip.
If your comment had been posted as an answer, with the explanation from the comment above, then the threshold for deletion would be much higher.