Thea's route being broken was a bug! It is supposed to be fixed in the latest version, but unfortunately requires an entirely new save to be able to unlock it (this is due to not really finding what was bugged, and simply rewriting that section of her route's logic) ^^"
There will be a Chapter 2! Once we finish all the content we have planned for Chapter 1 (you can check our roadmap on Discord) we'll begin developing Chapter 2 which won't be a different game, but will instead simply be released as further updates for Randel Tales :D