from what i understood, if both chain have consensus 50% from miners and merchants there is the possibility to have two coins, equally viable, and would be a problem to indentify the real bitcoin if something like this happen, with both of these coins with the same value at the beginning, and 50% after initial dump
If a 50/50 situation ever arises then I think the game is over. That's why XT, whatever you think of it, settled on 75% (which is still a little low) for two solid weeks before switching.
