The week I went clip-less, I nearly had that same fall. Somehow, my foot unclipped at the last possible second, and I caught myself. I haven't had that happen again since, but I think if I was in that situation again, I'd try to turn into the direction of the foot I unclip (providing there were no cars coming) so that I was at a less steep angle, then I'd either unclip, or try "paperboy" it up the hill (zigzag across the rode). If there were cars, well, I don't know what I'd do.