It will be difficult for Mexico to stop trading with the United States, as we are a large partner for them, but they are so mad at Trump I still think they will do it. He keeps talking about the scourge of evil Mexicans coming to the United States, and they aren't going to cooperate with that type of man.
Mexico will maintain its trade relationship with the United States even if Donald Trump wins the election. The trade partnership vastly helps Mexico's economy. While it can trade with other countries, the proximity and wealth of the United States makes it particularly beneficial to Mexico. Although there is a war of words, ultimately Mexico will not spite itself economically.
Despite occasional differences, Mexico and the United States are both important to one another. The United States is Mexico's primary trade partner. To attempt to cut off trade with the United States would hurt Mexico's economy far more than it would the economy of the United States. Mexico will continue to trade with the US.
The US and Mexico trade over $500 billion of goods across the borders. Despite Trump's "build a wall" policy and his poor polling with latino voters, I don't think Mexico could afford such a huge hit to their economic well-being. It may hurt US-Mexico relations, but it won't stop trading.