Here’s the problem: If the Supreme Court rules that Obama is ineligible BEFORE the electors vote, then they can vote for someone else - - no one is bound to vote for McCain, not even his pledged electors. So I think the Democratic electors would get together and choose Hillary Clinton. If there is a declaration of ineligibility after the electoral vote but before Congress counts the votes in January, then (assuming all electoral votes are cast as pledged) McCain is the only remaining eligible candidate.
If the U.S. Supreme Court rules Obama ineligible before the Electoral College, the only other candidate with Electoral votes would be McCain. They could only vote on McCain. It would be like the Obama ticket never existed. Up in the air might be what would happen to Biden. He might be the V.P. or the whole ticket might be disqualified.
The Constitution must be honored.
http://www.rallycongress.com/constitutional-qualification/1244