The commission on presidential debates stated shortly after Obama spoke that the debate will go on. If the commission says it and Obama says it, it will go on, I suspect. But we have yet to see which chess piece McCain moves next. Who can imagine that? Think of the most cynical thing you can think of, then double it.
Abraham Lincoln ran for re-election while leading the Union troops in the civil war. Franklin Roosevelt ran for re-election in the midst of terrible depression in 1936, a far worse economic crisis than we have right now, and in 1944 while prosecuting the second world war.
If John McCain can't debate while thinking about the country's economy, then he's even more ill-equipped to hold the job than I think he is. But of course he is capable of doing both. His proposal is not serious. It is just a rancidly political act. That he goes before cameras and tries to pass it off as nonpolitical, hoping that people will buy it, is what makes it contemptible.