Yes, McCain probably will and should bring up Ayers. The Obama campaign has signaled when Ayers does this, Obama is going to counter with Keating Five.
Fine. When he does, I hope McCain admits his mistake and should have a three-pronged answer ready.
1) McCain can say because of that terrible, terrible situation---which he was exonerated from---it has spurred him to be completely up front with his finances. And that’s why he accepted public financing, something Obama promised he was going to do through the primaries and later broke his pledge. This is the most important point among the three, IMO. (Full disclosure, I disagree with the concept of public financing).
2) He can bring his signature campaign finance reform legislation (I don't like the legislation, but heck, he believes in it, so it's fine for him to use.)
3) McCain can play up his efforts on GSE reform to push Fannie and Freddie to disclose more about their horrible finances. This links everything back to the current economic crisis and underscores why Obama can't be trusted, just like he couldn't be trusted to make good on his public financing promise and William Ayers and all the rest, to become president.