My impression is that in the lead-up to the election the international community and particularly the United States were operating on the following assumptions: that the elections would be legitimate, if minimally so; that Kabila would win; and that post-electoral violence would be limited, if only because of Congolese apathy and political cynicism.
I'm not sure anyone in a position of power would admit they were operating on those assumptions--especially now. But when I asked relevant people whether they were doing any contingency planning, they answered with a classic non-response: they remained confident, they told me, that the election would work out for the best.
Well, we're about to find out what happens if it doesn't.
Kamerhe and the minor candidates have already called for the election to be annulled. Tshisekedi hasn't, but only because early returns have convinced him he's going to win. Try explaining representative sampling to his followers if the tide turns.
But I also can't imagine Kabila giving up without a struggle. He'll sooner pull a Marcos and try to steal the election than admit defeat. Even if he were willing to step down, his people won't let him.
And this reveals the short-sightedness of the incom's decision not to take a major role in this election. Had the incom invested in elections on a scale comparable to 2006 to insure its legitimacy, Tshisekedi or Kabila and their followers might have been persuaded to accept defeat; I can't imagine either group will now.
How does this play out?
I don't know, but let me take note of a few things that might affect the outcome. First, I think the USG is invested in Kabila. The country is more or less stable, excepting pockets in the east--and even there violence is declining. People (read: Western mining companies) are starting to make money. And the State Department has despised Tshisekedi since the Cold War, when his mere existence was a standing rebuke to the diplomats fellating Mobutu. If there's a plausible case to be made that Kabila has won a legitimate election, the incom will make it.
Second, I can't see the incom dispatching peacemakers to stem the violence, if it breaks out, no matter how bad it gets. Western politicians' primary concern is with voters back home, and they won't see any percentage in intervening. Kinshasa can burn to the ground without costing Obama a single vote; but one dead American soldier could tip the election against him. The lessons from Blackhawk Down haven't been forgotten, whatever politicians say when they're visiting Kigali's genocide memorial.
Third, the flash points in this conflict will not be in the east. They'll be where the election is most keenly fought: in Kinshasa and in the regions in the southeast of the country, where the peoples of Kasai and Katanga mix. There is history there, going back through Katanga's secession to the days of Tippu Tip. It won't be pretty.
Finally, we are approaching the point where perceptions become more important than reality. Soon, it won't matter if most of the problems with the election turn out to be separate incidents, and not part of some generalized effort to steal the election. It won't matter if the international community decides that, on balance, the election met some minimal level of acceptability and declares it legitimate. What will count is the perception on the street. And that is getting darker by the hour.
 To say that they were operating on these assumptions is not to say that they believed in them. I don't think they failed to make contingency plans because they are incorrigible optimists. I think they failed to make plans because they knew they lacked the resources to respond adequately if things went badly. Welcome to the end of the American Empire.