Or if the Libertarian who showed up had used a little common sense and voted Republican in a tight race...
In a democracy voters have a choice of whom they want to represent them. I won't presume to dictate those choices to others and would expect the same in return.
Non-voters on the other hand don't make any choices. If you need to assign blame for a particular outcome, its the non-voters in your own party who are responsible.
How are the libertarians supposed to know that the republicans aren't going to show up for their own candidate?