The Mayan language and culture have been in continual use by the indigenous people of the region for thousands of years. The Aztecs, the Mayans, the Incans...all their languages and cultures are still thriving, but under the rule of the nation-states that Spain left behind. As for other "disappearing" peoples, they're all over the place, especially in the Americas. As a linguistics major, I can tell you that the vast majority of Native American languages are extinct or heading in that direction. The most widely spoken of them, and one of the very few with a body of speakers that is actually growing, is Navajo, which only has 100,000 speakers. Most of the Native American languages which still persist have a few dozen elderly speakers at the most, and scientists are scrambling to find out as much as possible about their languages and lifestyles before they vanish off the face of the planet. Fortunately this is not so severe in Central and South America, but it doesn't look like many of these tribes have much hope of retaining what they have left for very long.