I find this scenario extremely rare as in most cases I'm envisioning, there is a middle turn lane separating the two opposite lanes. Either from a light or just as a buffer between the flows of traffic.
This is all to say, there aren't any hard and fast rules and there are too many scenarios to cover with a blanket statement like "The left lane is for passing. If you're not passing somebody, move over to the right lane. It's not that hard people" (comment above).