Dean would call Sam for back-up. It was almost guaranteed. Which would get both Winchester brothers on the scene. They were prepared for that. In fact, they were hoping for it.
The ritual to trap a local reaper was all prepared and just needed a few incantations to call the reaper and trap it.
Jo's voice was panicked, high.
"I don't know. I just woke up in the woods near the gates. I'm hurt. Dean, you need to come get me. I think-"
The phone clicked off. Jo's lips curved into a smile as she let the phone turn off entirely.
If that didn't get him here, they would resort to more desperate matters, but they were confident that Dean would fall for the ruse.