They 'almost' admitted that he had left a note, but backed away from confirming it. I sort of hope he left some sort of explanation & goodbye. I assume we'll hear eventually.

That program I mentioned had a long interview with James Lipton of The Actor's Studio program. He reflected on his attempt to interview Williams, but noted it was 6 minutes before he was able to ask a question.
Then they played my favorite clip ...of Williams taking a scarf from an audience member and doing 5-6 minutes just giving his only way of answering a question about how his mind worked. (Someone said he was always composing the next 'bit' as he was working thru the current one. It reminds me of translators who can listen to one language and speak another one.)