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It will depend on the tax reporting type that the LLC will use. Corp, partnership, or disregarded each have their set of rules. This is an older article from The Tax Advisor but may be helpful: https://www.thetaxadviser.com/issues/2009/oct/contributionsofpropertytoanllc.html

Maybe so, but I'd still try file as it stands first before contacting the widow. It's my understanding that in most cases it is the funeral home that notifies the SSA of death, so TP's account may not yet be locked. If the return does get rejected, it is only then to add the DOD and indicate that spouse's signature is as surviving spouse on their joint return. That 8879 doesn't go anywhere but in the preparer's file anyway, and this rejection is easily explained and corrected if necessary.

See what others say, but I think you can file it. TP signed it before his death with intention that it should be filed. If TP had still been alive, signed it, and dropped it in the mail to you and you just received it, you would file the returns when you have the signed form in your possession.