Let's pretend that the Europeans are somehow too distracted by some factor to find the Americas. Could the Aztecs and the Incas, the greatest Native American empires, expand enough to meet and possibly conflict? Or would internal problems destroy them before any contact is possible?
I don't think so. Even if there's no European collonisation, the Aztecs would have collapsed long before any contact is possible. The Inkas havee a better chance of surviving, but their empire still faces the risk of disololution due to a civil war, simple overextension, or the rebellion of some of the peoples submitted to the empire.
However, I believe that, if there's no European colonization, the Andean war and Mesoamerica would get in contact, let's say, by 1800 AD. These two worlds might or might not be political united when that happens, but they would certainly be united culturaly and economically.
I believe that if the Europeans don't show up, the Inkas would get into Colombia's highlands, incorporing these lands into the Andean world. I think that such an expansion would be more likely that an expansion into Argentina (at least in the short run), as the Inkas prefered to incorporate to their empire lands already heavily populated and inhabited by people who knew agriculture than areas sparsely populated occupied by huntergatherers (as was the case of Chaco and the Pampas, the areas that bordered the Northwestern part of Argentina -the part the Incas conquered IOTL)
It's not illogical to imagine an Inka sucessor state getting in touch with whoever runs Mesoamerica by 1800 AD, either through the Pacific, Panama Itsmus or the Caribbean Sea.
When that happens, both centers of civilization would benefited greatly. Mesoamerica would get potatoes, quinoa, Guinea Pigs and Llamas. The Andean world would get writting and other stuff (like notions of urbanization, building techniques and some comercial practices which were more developped in Mesoamerica).