is there a statue of limits to a case like this a person who a guardian who chooses to pull the plug for insurance money?

Statute not statue.  Are you the one who did this, if not do you have proof of this?  You are stating a lot of accusations, it is also against the law to get someone in trouble and lie about something without proof.  Be careful, I hope you are not the one who is planning this because it doesn't matter how you commit murder there is no statute on murder.

How do you know this person was after the insurance payout?  Have you ever been in this situation?  I have and it's a heartbreaking decision.  Don't assume the worst.

That is indeed criminal, yes.

the local district attorney might be interested.  and there is no statute of limitations for murder

You would find it very challenging to make a murder case out of that. At best you'd get something along the lines of criminal negligence, because they made decisions that led to the person's demise, but did not play a direct and active role in their death, which was due to underlying medical conditions. And, obviously, if the charge is anything less than murder, there's a statute of limitations.