A couple of more points:
1) The political advantage of Plan B was that it could have shifted the focus to Senate Democrats and at least set them up to take some more of the blame if we go over the cliff. Now Republicans will be even more vulnerable to getting blamed.
2) If part of what President Obama was after was Republican humiliation and disarray, it’s going better than even he could have hoped.
3) It’s possible to envision a scenario where, in theory, going over the cliff enhances GOP leverage. But the emphasis is on in theory. As soon as we go over the cliff, Senate Republicans will almost certainly start peeling off and House Republicans will be even more isolated. Then, they will likely see defections in their own ranks, too, and buckle in a pell-mell retreat.
4) Boehner is in an intolerable position. Either he has the confidence of his conference or he doesn’t. It was a risk to announce Plan B before he knew he had the votes. But if his members don’t have his back in such a high-stakes situation, well then, something eventually has to give.
5) The GOP leadership seemed united on this one, but there’s nothing like a debacle to create an every-man-for-himself dynamic. I wouldn’t be surprised to see tensions begin to emerge between the camps of Speaker Boehner and Whip Kevin McCarthy.