If he didn't sell his soul post 2000 he could have ran as a independent in 2008 and possibily won. Remember there was a day when there was no politician more highly beloved by the public than John McCain.
If we didn't have the stupid closed primary workings that we have today and general elections were basicially open primaries with winner take all McCain would have been elected president in 2000.
This is why I think he considered switching parties, 2000 McCain would have gotten a huge warm welcome in the democratic party back then and had a very good shot at getting the '04 nod from them.