The Retina 12" MacBook Battery is integrated into the bottom case assembly. Apple replaces the entire bottom case in order to change the battery. Because the Logic Board is also secured into the bottom case on this model, that means a battery replacement is essentially a complete teardown and rebuild of the computer, with the exception of the Top Case and Display.
So there is a procedure there, but I wouldn't expect it to be easy or cost effective. Apparently Apple offers fixed price battery replacements in some regions that will offset the cost.
While technicians have had success in removing the battery from a Retina MacBook Pro without exchanging the top case, it would be far more difficult with the Retina MacBook. The terraced cells don't work in our favour in this regard.
As long as Apple continues to supply parts, sure. As soon as Apple stops supplying replacement parts for a machine, generally somewhere around five years, I wouldn't count on it being possible. That said, some of the more creative and adventurous types in the repair business have surprised me before, so who knows what will happen.