Pretty Sharp til the end. The fact that people were still listening to what he has to say about investing in Alibaba as recently as this month is actually pretty nuts (in an impressive way).
Was he? I listened to an interview of his a year or two ago and he didn't seem to be all that sharp at point. Amazingly sharp for a guy who was almost a hundred, sure, but not relative to a typical 80-year-old. He must have been amazing when he was younger, though.
I think it depends on what you mean by sharp. Quick? No, physical capabilities. His understanding of companies/markets/etc still were considered quite sharp by most investors I know.
time will tell. I don't think there is anything to vindicate here. Also, really smart people are wrong about a lot of things all the time - being wrong about one thing should not diminish your other contributions.