A master never stops teaching. If no one was around he'd be teaching the insects taisabaki. That's the reality of someone like him. The reality of that position and type of person is what needs to be understood in my opinion not what bill or jack said.
I have a friend and when he hasn't been seen for a while and students complain they are missing him and ask where he is I just laugh and say he's somewhere no doubt teaching someone something.
Sure. But if Ueshiba Sensei is off teaching tai sabaki to the insects in Iwama while Saotome Sensei is training in Tokyo, Saotome Sensei probably isn't learning much from him. The question is not whether Ueshiba Sensei was teaching, but what and to whom.