Based on how the story Nancy and Jonathan was going, and how it seems she still pines for Steve - I could also see Steve being the one to go instead. But basically, one of her boys is going.
AFA Lucas, I think the main kid group has gotta take a hit. I think Mike and Dustin are too untouchable; and if Jonathan dies, they can't kill off Will. Plus, it creates more loss for Max which could further her character development even better for the 5th.