I see this is a very popular topic, to be sure... As for a more specific PoD, I think a victory for the Snake Kingdom at the Battle of Yellow Rabbit Place in 695 would do a lot to bring stability to the region. One of the big problems later on was instability, and personally I think the weakening of what was formerly the strongest Maya kingdom had a lot to do with this. Of course, the betrayal of Dos Pilas and the creation of their Petexbatun kingdom certainly exacerbated things, and even if they were a thorn in Mutul's side they certainly didn't help with the general problems of instability.
I wonder though if most of the Maya could form up into a confederation, like the later League of Mayapan that had most of Yucatan joining them. There is a theory of how Classic Maya were organized that could help with this. One theory states that they were organized into at least 13 regional provinces, or Tzuk', much like how the Postclassic Maya of the north were organized into 16 or 18 "Petty States". The idea was that each Tzuk' represented an ancient kingdom and the capital of each were all principle cities that competed for rights to host the cycle, that is the 256 year calendrical cycle called the may in later times. The cycle seat would have many rights and privileges, and cities in their Tzuk' would rotate seating each katun, or 20-year period. Obviously this wouldn't make very much sense given the violent competition and warfare, especially over more mundane matters like resources, we know happened throughout the Classic Period. The theory states that this form of government existed alongside the typical hegemonic networks of states and vassal states we know so well. Granted, I think it's a bit dubious to believe they had the may cycles and calendrical governments like in the Postclassic, but it's an interesting theory nonetheless and I kinda wish the idea about there being 13 or so Tzuk'ob is true because that would make things so much easier for me. And of course it would provide a good framework for a more united Maya if that were even possible.