Originally posted by renlish:

When they update the biomes you're going to have to seed a new map anyway. There's a mod that allows you to save/download builds so if you grab that and save what you have so you can just drop it in again if the official release does clear all maps. That's a LONG ways off, though.

This hasn't been 100% confirmed yet. But if you build on the unfinished biomes you could probably expect that to be destroyed.