Unless the city and/or county is willing to come up with some money same as Cal Expo is (a State governement entity) it's not likely to be at either the railyards or Natomas. If the arena is built at Cal Expo, that also means the Maloofs can raze Arco, sell the Natomas site and have money to pay off the balance of the city loan provided to prior ownership and have some mony to apply toward the new arena at Cal Expo.
After years of trying to get the city or county to do something, there isn't much sense that the city/county can manage to pull off anything.
If the Cal Expo site fails, then city-county money and willingness is the last resort and is not very likely to happen, if a 10-year history has any predictive value.