What do you think Shawn means when he says “Am I the done deal?” in Stuck in Neutral?

Shawn's mom and his sister, Cindy, are about to head off with Cindy's friends on their trip to Spokane, leaving Shawn alone with his dad. Just before the party's about to leave, Shawn's dad casually mentions to Vonda, Shawn's caregiver, that he'd like to stay overnight with his son. Shawn overhears this and is immediately worried. His dad has never once stayed with him by himself overnight. Why now, all of a sudden?
That's when Shawn starts to wonder if he's a "done deal." In the context of the story, what this means is that Shawn thinks that his father might somehow try to kill him. It's reasonable for us to make this assumption given that Shawn spends a lot of time in the book genuinely worried about the possibility of being euthanized.