Does it have to be official - witnessed and notarized? How about a casual note with final wishes and it's signed at the end.
If it is (1) dated (2) signed and all in the deceased's own handwriting it is a valid "holographic" will. Your facts seem to indicate it is not dated. If not a valid holographic will, two witnesses are necessary but not notarization.
The above is general legal and business analysis. It is not "legal advise" but analysis, and different lawyers may analyse this matter differently, especially if there are additional facts not reflected in the question. I am not your attorney until retained by a written retainer agreement signed by both of us. I am only licensed in California. See also avvo.com terms and conditions item 9, incorporated as if it was reprinted here.
Estate Planning Attorney
Under the right circumstances a fairly "casual" note that's signed and dated can be admitted as a will ... as long as it's entirely in your own handwriting. It can be on the back of an envelope if it says "this is my will. Give all my property to (name)." .. I got one like that admitted to probate a number of years ago.
BUT, it would be better if the will were more formal - that way, it's less likely to be challenged. And since there are no "do-overs" after you're gone, if it's important to you that your assets go to the people (or organizations) you want them to go to, then it should be important to you to do it right.
The response given is not intended to create, nor does it create an ongoing duty to respond to questions. The response does not form an attorney-client relationship, nor is it intended to be anything other than the educated opinion of the author. It should not be relied upon as legal advice. The response given is based upon the limited facts provided by the person asking the question. To the extent additional or different facts exist, the response might possibly change. Attorney is licensed to practice law only in the State of California. Responses are based solely on California law unless stated otherwise.
If it is not in your own handwriting, it does not qualify as a holographic Will. It would then need to meet all requirements for a formal Will, which your note probably does not. If all of the beneficiaries are in agreement, (Including the ONE beneficiary from the old Will), you might be able to have the note admitted to probate. Otherwise, I think it will be tossed out.
This is one of the MANY MANY examples why it is so critical to see an attorney to get your estate planning done right. Otherwise, whatever you leave behind might totally fail to realize your objectives and your wishes and intent will be thwarted. Estate planning is not a do-it-yourself project!
*** 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.