I just sent Alaska Airlines an email asking this question, but figure I might get an answer here even quicker.

I was just trying to book a one way from Anchorage to Las Vegas using the website. There appears to be no way to book a one way trip using the mileage plan - which seems odd since Alaska has been touting the ability to split flights into one way segments.

Since they dropped the non-stop to Vegas, the cheaper non-stop on US Airways looks more attractive for a return since it leaves at a reasonable hour. But Alaska has slightly better flights in the morning TO Vegas.