There are places that are appropriate for folk with dementia, but IMO a law office is not such a place. What liability? What if he injures himself? What if he interacts with clients in some unpleasant or inappropriate manner? What message does it send to younger staff as to the office’s standards? What does it do to this guy’s image? Believe me, the newer hires are going to hear tales of how great he was, but then juxtapose them with what they see.
Hell - if the guy is as dotty as it sounds, maybe the firm should rent an office nearby and just TELL him it is his old office!
Keep him separate from current clients and people who are trying to work.
Law offices can be highly competitive and often mercenary (I don’t know how large the OP’s firm is, or what type of law they practice.) Often associates are constantly pressured to bill more and more, in the hopes that hey MIGHT someday make partner. And yeah, often the partners - at least the rainmakers - are rewarded lavishly. Personally, I’m not a fan of such a system, but that is my impression of how it often is. Where in such a system do you factor a senile old partner?
When I was assigned to my present office, one of the judges was clearly no longer capable of performing his job either physically or mentally. People who had known him years back would tell me how impressive he USED to be. That’s all well and good, but for the entire time I knew him, he was stealing his salary, and poorly executing his sworn duties.
IMO, his wife - who drove him to and from work - was using the office as a babysitter. Which may be understandable on her part, but offended me to the extent it took up scarce resources those of us who were competent could use.
Since he had such seniority, he had priority in certain things, such as preferred dates for holding hearings in the shared hearing rooms. So he squatted on some of the most in-demand hearing room slots, while producing very little work - and what little he produced was of very poor quality.
If he and his wife were not wiling to have him retire, our office should have declared him unfit (it CAN be a challenge to fire this sort of judge.) But instead, they assigned him work in a manner that he fell short, so it was a protracted and ugly process.
Then, when he was finally gone, his work was assigned to the rest of us. EVERY SINGLE case of his was incredibly fucked up in one way or another. The waste of office resources and the imposition o claimants was incredible and IMO inexcusable.