So far almost every update has worked like this:
- your saved game (map and character files) are fine
- explored areas are locked. Unexplored areas are updated and regenerated.

and my advice is to not explore far into the incomplete biomes (currently far north and ashlands, one is all ice, the other all fire currently) so that when those are completed you won't have explored regions that remain empty.

!The ocean is also a biome, so exposing every inch you can of it may be an aggravation to you in the future.

regardless, so far, we have not had our stuff wiped out very often. I can't recall it happening at all, but I came in after it had been out for a little while and don't know the very, very early game history.

** some people using mods have had some issues. Also a few people have had their bases mangled by terrain resets, which I am not sure if came from mods or if sometimes the explored/locked thing does not work right. So be aware that a few people have had issues for one reason or another, but most people seem to have their stuff intact across the last couple of years. Mods are not sanctioned yet because its EA, so they are basically hacks that do what they do, use at your own risk and expect breakage on update.

Finally, we just had a major update. I would not expect another for a good long time. So your work should be safe for months, more than enough time to beat all there is to do. I do expect to eventually have a release day where we may lose it all and have to restart. But that looks to be a couple years off.