One reason why you're still able to function is that you don't rely on your sense of depth that much these days. i.e. You don't need to gage where a spear or arrow will land. Even in a car, you are effectively on a one dimensional track and only have to decided to go left or right.

If you only had one eye, then in situations where there is lots of pressure to perceive depth I think you'd have to move your head around a lot.

Which makes me wonder, which human activities demand the best depth perception?