I just hope my instincts would kick in well enough ahead to make the right decision. Tough call, that one can be... and not a lot of time to think about it.
In military aviation they train you to think through emergencies and make up your mind what you're going to do before the situation actually happens. Then, when the situation happens, you already have a plan. All you need to do is execute the plan.
There is never time to think it through, and indecision has probably killed as many people as anything. I have some general rules but I often update them in traffic. For instance, "Where am I going to go if that idiot turns left?" or "Is there room on the shoulder if that moron pulls out?"
Of course, nothing is fool proof since mother nature is always cranking out new and improved fools.