There's no realistic trade that would make sense for Dallas to do. Not to mention the full NMC. The worst thing they did was hand him that contract after what will likely turn out to be a career season. However, there weren't many other options at the time. Very few teams allow their best players to leave if they want to stay, regardless of what that means for the future.
The Stars knew what they were getting themselves into. They're just going to have to live with whatever Benn is. Likely for at least the next 3 years, after this one. Probably until 2024 at the earliest.