Unlike the mindless Republibots around here, I am actually capable of looking at the polls and seeing whether my vote is going to matter or not.
If you're in Illinois, it doesn't matter who you vote for, Obama will win the state.
If you're in Wyoming, it doesn't matter who you vote for, Obama will lose the state.
If the electoral vote polling shows that Obama is going to win no matter what, you may as well not waste your vote on Romney.
If the electoral vote polling shows that Obama is going to lose no matter what, you may as well not waste your vote on Romney.
The ONLY time it matters whether you vote for Romney (or against Obama) is when your state is close AND the electoral vote count overall is close.
ETA: in the impossible
situation you depict, if it mattered, I'd vote for Romney/Paul and hope Romney dropped dead of a heart attack in excitement at having won.