I don’t think these rules will apply since the removal of 0bama would be post-election. It doesn’t seem logical to allow the dems to pick another NOMINEE after the election itself has been ruled invalid. I would hope the SC would simply say that McCain was running against an unqualified opponent which is the same thing as running unopposed, ergo, McCain wins the election.
The election wouldn't be ruled invalid. Only the candidate would be ruled ineligible. That may not seem logical, but rember we didn't really vote for a candidate or a slate, we voted for electors pledged to that slate. The laws of many states require not voting for the candidate whose name was on the ballot, but rather for the candiate of the party whom they were elected to vote for. Californial for example.