OK, last night I drank the last bottle! It had been bottled since early November, so let's say 5 months. It had been a month or two since I'd had one.
It was still very good, but it was noticeably different than when it was fresh. I did swirl the yeast and pour that into the beer. A lot of the banana yeast esters had faded, and there was a much more prominent dark caramel/toffee flavor. I liked it better fresh, my GF liked it better this way.
So... use this information how you will