I would wait until you close the estate to shred any documents. When someone passes the Power of Attorney ceases to work. It's a document that allows you to act for someone while they are living. Once they die, the document dies also. The will takes over at that point and if you were appointed as the Executor (male) or Executrix (female) of the estate then you would need to file the will with the court house and begin the job of representing the estate. If your nephew contests the will or your actions as the attorney in fact (agent), under the Power of Attorney, you may have to produce records to substantiate your actions.
Hold on to POA papers and any records of anything you were involved with as POA.
You can be held accountable for your actions as POA.
The answer given does not imply that an attorney-client relationship has been established and your best course of action is to have legal representation in this matter.
I agree with my colleagues. I see no benefit to you in shredding these documents and in light of the pending contest, it presents a red flag that implies that you did something wrong that you are trying to cover up. Even though the documents have not yet been requested, it does not mean they will not be in the future. I would hate to need to tell a judge that I shredded some relevant documents. Just hold onto them for now.
You should have an attorney to represent you, given the Will contest. The attorney can advise you regarding your records, as well. Best of luck to you, and I hope that the court proceedings are brief and uneventful.
*** LEGAL DISCLAIMER I am licensed to practice law in the State of Michigan and have offices in Wayne and Ingham Counties. My practice is focused in the areas of estate planning and probate administration. I am ethically required to state that the above answer does not create an attorney/client relationship. These responses should be considered general legal education and are intended to provide general information about the question asked. Frequently, the question does not include important facts that, if known, could significantly change the answer. Information provided on this site should not be used as a substitute for competent legal advice from a licensed attorney that practices in your state. The law changes frequently and varies from state to state. If I refer to your state's laws, you should not rely on what I say; I just did a quick Internet search and found something that looked relevant that I hoped you would find helpful. You should verify and confirm any information provided with an attorney licensed in your state.