Sunstone,the Mayan culture at its peak was not unlike, say, the Egyptians or the Romans. The most advanced in their region. Like the Egypians and Romans the Mayans conquered other cultures and spread out. My fellow posters above me have given reasons for the demise of the Mayans and I do not dispute them for at the very least, what they say no doubt has truth in it.
My part of what may be true is that the dominant culture (Mayans) became complacent. Technological advances and conquered lands to draw resourses from would make life quite comfortable. Survival no longer being an issue of great importance, matters that are trivial would become more important (entertainment, self indulgence, personal wealth, individual rights, ect). Quite simply, complacency breeds contempt and contempt breeds the demise of unity.
To answer your question, yes they could have prevented their demise. Once a comfortable living was established, they could have turned their attention more towards Self-developement (seeking inner peace, lovingkindness, forgiveness, Oneness, ect) Many did of course, and anyone who has studied the Mayans must me in awe of their astrological knowledge. It still rivals what we know with todays technology. Unfortunately, too many chose the path of self, rather then Self. I'm guessing what you really want to know Sunstone, is if it is to late for us. No, I don't believe so, but it is hard to deny that we may be very close to that edge. Let's do what we can to change things before it's too late.