Camera obstructions are big problem, yes. A combination of hardware fixes (making it less likely for obstructions to happen in the first place), redundancy, and

Camera obstructions are big problem, yes. A combination of hardware fixes (making it less likely for obstructions to happen in the first place), redundancy, and detection of the issue coupled with an escape plan, is the general approach to fixing it. (the escape plan is a big one: a lot of effort goes into making sure the car can stop/pull over safely if something goes wrong)