I avoid clipping out on my MTB (SPDs)...I grab a tree or fence and hang on to wait for whoever I am riding with. If it is unavoidable, I clip out early. But man, I fell over a lot until it became automatic (usually on hills where I was struggling to keep momentum...once I struggled so hard up a steep incline that I actually pulled the bike over backwards on top of myself. I was a sight...head pointed down the hill, on my back, doodlebuglike, still clipped in. Someone had to come rescue me when he stopped laughing).
On the road bike, I am currently changing my dang pedal set up, so I see plenty of stop sign tip overs in my future. My mantra...protect the bike.