moish, it seems you are concerned about how prosecution in the Hauser or Neumann (the WI girl above) cases would keep frum Jews from practicing their religion. How exactly do you envision this happening? Note that in both cases the government intervened because the parents withheld standard-of-care medical treatment for ostensible religious reasons. This is because the government is responsible to protect the health/ safety of minors when their parents refuse or are unable to do so.
Which religious Jewish practices involve withholding standard-of-care medical treatment? I can’t think of any, and am not seeing the slippery slope that you seem to fear here. The example of a patient being removed from life support against the family’s wishes is completely unrelated Iof anything it’s sort of the opposite), and prosecution in the cases above would in no way create a precedent.
Personally, I don’t know much about cancer treatments, but for a child to die of DKA (which probably took about a month) because her parents prayed over her instead of bringing her to a doctor is unconscionable.