" If a physician has 'officially declared' a dementia diagnosis - it could be dicey having the taxpayer sign anything."

Many patients are diagnosed with dementia long before they lose so much mental capacity that they can't appoint someone else to take care of everyday business.  And it is rare (to say the least) for IRS to "get dicey" with whether a Form 2848, or power of attorney delegating tax matters, is valid.  What is the auditor or revenue officer going to do -- demand to deal directly with the taxpayer they are claiming is incompetent?