Should the federal government intervene if a state allows the euthanizing of people over who are on feeding tubes (umbilical cords) without their informed consent and/or due process?
The federal government can enforce the 5th Amendment due process clause against a State, to protect persons, so the answer to your question is, if it's without due process, yes. But what do you mean by "without due process"?
That's an extremely vague term, "due process", and I have seen it twisted. Scalia probably hates it, as do I.
If the State acts with "due process", then the answer to your question is no.
A State can allow a doctor to perform an abortion, say in the case of rape, and it will be acting with "due process", as far as I'm concerned. Due process means you considered the mother's and the child's 4th & 13th and 5th Amendment constitutional rights respectively, and found that the former outweighed the latter, early in the term. What do you think due process is? I think it implies that a law was passed or not passed in accordance with the State's or US Constitution.