He wanted to debate Ryan (6? times). When Ryan dropped out he dropped down to debating Keyes (2? times).
As far as I know the debates happening are a done deal.
Yeah, because he wasn't doing so well against Ryan. If you want to know what a politicians internal polls are telling him about the race look at how often he wants to debate. Remember how right before the RNC Kerry put out a demand for a debate a week. Remember when Gore did the same thing. The guy behind always wants more debates, and the guy ahead always wants less.
Until the debates actually happen they aren't a done deal. If Obama has any political savvy at all he'll find a way to get through this campaign without any debates, not because of how good Keyes is but because of raw political math. At this juncture the Keyes campaign is underfunded and under organized, the smart move by Obama is to avoid giving Keyes any shot at equal time. While he might lose some points for being chicken it won't be nearly as many as he risks for being brave.