So I did some research, Wattpad isn't deleting unfinished stories but if you haven't updated in six months or more they'll send you a message that goes like this.
Hello!
Our system indicates that you have a story which hasn't been updated in a while. Our readers tell us that one of the biggest issues they experience is starting to read a story only to find out that it has stopped updating and has no ending.
If your story is complete, you can go into the “story details page” and mark the story as complete.
If your story is not complete, consider updating it as our discovery
(It's an automated message)