The expected behavior in the oncoming lane is to slow down (not stop), and use the breakdown lane/margin or whatever you want to call it to make room (in the case of a truck blocking half the lane)

In the case the truck is blocking the whole lane, it's typical too stop, wait for a clear shot, and then go, if oncoming cars appear they stop, the next car that would leave their lane stops, and the oncoming cars resume their right off way when clear...

Pretty sure it's an unwritten protocol, but that's how it would work smoothly and preserve right of way. You can't account for people breaking the protocol though, there's always that one guy... People have trouble when two lanes merge to one as well, you're supposed to create a space for a car between every car, and once you get to the merge spot it can be smooth like a zipper closing, but there's always that one guy that won't leave a space and stops traffic in the other lane.