Yes, the parents should be punished. Can they be punished? I don't know. How much are they paying their lawyer
But on a serious note, they should be. Why, because their ignorant enough to refuse modern medicine techniques that can save their child from dying on the account of blind faith in beliefs that cannot be verified as true or even be proved to have been stated by someone at that. Using the practice of prayer is fine but why not incorporate it with the modern medicine techniques that have been developed for us by us. To assume or believe that the Lord would not want us to use our own technology along with the power of prayer to save a life is a bunch of horsy poop for the ignorant at the shallow end of the Christian pool. The more intelligent "disciple" would believe that the Lord has put in us some of his knowledge and understanding so that we may live better lives.
Even if the chance of success was only 20% and the little one dies the parents could still be given blame. I would also make it a personal goal of mine to convince the sorry excuses they have sinned beyond are world and will be punished personally by the Lord. As a Christian, I believe they are sinning. The Lord has provided us with a wealthy amount of evergrowing knowledge and they throw it away in their own cheesy interpretations. No matter the chance of success, if there is a chance it is there responsibility to take advantage of the blessing and hope that it heals their child. Not doing so is irresponsible and very stupid for the day and age we live in.