In a sense I think there is some promise to the street marches that have begun over the past few days in that they could help to force a recount of the votes, which should be seen as essential to any election as close as this one is. However, if Lopez Obrador and his supporters do not accept the result of the election after a recount as has been suggested they wont (assuming there is one and that it is open and fair), then the civil unrest they will cause would be far worse than the results of a Calderon Presidency.
It was a bad year for the PRI which ruled Mexico for more than 70 years, as the news cycle this year consistently burned that party, they lost support in Oaxaca thanks to a heavy handed response to striking teachers, new evidence emerged that they had assassinated political opponents in the 1960s. The PRI could recover, overcoming its history of corruption and authoritarian tactics to become a respectable centrist party. But if they do not, the PRD has many votes still to gain from former PRI voters. The PRD should continue to build up its support running strong candidates for all offices over the next 6 years and running another strong candidate again in 6 years, perhaps even Obrador again. Obrador lost this election by refusing to participate in the first debate, which allowed the "Obrador will wreck the economy" frame to dominate the public discussion, it was a huge tactical error. In spite of the loss that Obrador has likely endured, this election was a victory for the political left in Mexico, the PRD gained legislative seats and is a legitimate opposition party, potentially even a majority party if they can align themselves with the PRI (which they were once part of) in the legislature. The fact that we were seriously talking about a legitimately liberal President in Mexico is a huge step forward, if the PRD continues to build in this way I have nothing but hope for Mexico's future, for this was a victory of political legitimacy for Mexico's poor overshadowed in her history only by the Revolution.