We won't be deleting registered accounts when we move to Steam Early Access, so as long as you have registered your game account - with an account name and password and e-mail and all - your character is safe. (An in-game account is NOT the same as a forum account! Basically if you enter a username and password when you log into the game, you're fine.)

Now you will need to connect that account with a Steam account, and you will need to purchase the game (or have gotten one of the packages), but your character will be waiting for you when you do.

We will probably be deleting unclaimed guest accounts - accounts that don't have a name, password, and e-mail attached to them - at some point in the future.

Edit: Changed 'wiped' to 'deleted' for better clarity.