But one candidate did receive the required 271 electoral votes - Obama. So the 12th Amendment does not apply.
There is a very distinct possibly that we could end up with a McCain / Biden administration. Primarily because Congress is not able to introduce new candidates for President as part of their participation in the resolution of a non-majority election. Biden would be a new candidate for President as the VP slot is handled via a separate vote.
There is no chance whatsoever of McCain winding up as either president or vice-president. McCain lost, he's out of the picture. Worst case scenario, Congress picks the President and the Senate picks the vice-president per the 20th Amendment. The Democrats control the most Congressional delegations and they also control the Senate. Most likely scenario, Biden is president and picks a vice-president.