A win pretty well assures it. If we draw, we probably end up playing Honduras in the semis, while a few points behind El Salvador. A draw against the U.S. and a win against Honduras would put us back into the Hex, but I'm not sure if it would put us so far ahead as to guarantee a spot.
Just as a side note, people are too worried about Curacao I think. Even if they get past Costa Rica, they'll probably have to go through Mexico in the semis. Our chances of playing them our very low, in addition. As long as Mexico handles Panama, and Honduras doesn't completely blow it against Trinidad (and assuming we get past the U.S.), the semis will be Canada vs. Honduras and Mexico vs. Curacao.