The exact extent of Human Sacrifice in the Aztec Empire, and Mesamerica is somewhat unknown. Furthermore the culture has suffered from all types of exaggeration, in both the low and high ends, and has sometimes even been romanticized. Nevertheless it became a huge detriment to the survival of Mesoamerican culture once the Spaniards arrived.
With the creation of the "flower wars" in order to sustain it the Aztecs preatty much had turned all of Mesoamerica against them. Wich resulted in the Tlaxcaltecs siding with the Spanish.
So what if there had been no human sacrifice in Aztec and Mesoamerican culture over all?
It is hard to tell how big a difference in population it would create, most likely it would be at least a bit higher.
But it does bring the possibility of having a much more united Mesoamerica, maybe the whole centre of Mexico could be united under a single Empire. If it was what would it's chances be of avoiding Spanish conquest?