If the ESP company "voids" the contract, then they should be required to refund a prorated portion of the cost of the contract. However, my understanding is they will refer you to the selling dealer to initiate the refund process, and you are unlikely to receive a refund of the amounts that constitute the commissions that the MoCo and the dealership rake off the top. In other words, if you are halfway through a five year contract, don't expect to get back half of what you paid for that contract.
Regardless, I'd insist on a refund anyway, even if it's a tiny percentage. Why let them keep profits they didn't earn?
Considering all the people with the exact same contract who have received ESP repairs with much more in terms of modifications than just a set of mufflers and a tuner, I have to believe someone with a lot of money and time and determination could prevail in a court of law. I'm pretty sure there has to be some legal requirement for them to treat every customer equally, rather than arbitrarily as in this case. But who really wants to be the guinea pig?
Jerry