This is a new one on me. Your issue is whether or not the post on Facebook would be sufficient to constitute a revocation of the Will. I see a number of problems with your argument, not the least of which is proof. Since YOU were able to hack into his account, where is the proof that your father was the one who made the post in question? I think you may have a really difficult battle on this. I see very little chance of your winning this unless you have a very skilled probate attorney to assist you. Very tough case.
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I agree with Attorney Frederick-very difficult case and unlikley that facebook posts would be valid.
I would start a probate as though he died without a will and see what happens next.
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.