This question was triggered by a review of this low-quality post. I dropped a comment explaining how to favorite the question in the sincere desire to help provide some clarity. I've reviewed http://meta.askubuntu.com/questions/8083/how-can-i-view-a-comment-for-a-deleted-answer and http://meta.askubuntu.com/questions/3439/what-happens-to-my-comment-if-the-parent-question-answer-is-deleted but I'm not certain exactly what happens. Does the comment stay in the users inbox even after the post is deleted? Disappear into the ether?
They can see it, but they will not be notified of it. This is explained in this post on the main meta, the relevant part of which is:
When an answer is deleted, only comment notifications to the OP left by the deleting moderator within that last hour will remain in the inbox.
[ . . . ]
Since notifications are cleared after the answer was deleted, commenting on a deleted answer would indeed keep the notification, which is reasonable as only moderators can comment on deleted posts and users can see their own deleted posts.
Comment notifications are deleted when a post is deleted, so unless you're a mod, your comment will not notify the OP.