Does the story end when Cassie is saved?
No, it only ends if you do it the fast way, it gets complicated if you wanna save cassie and continue the story, and to be honest, currently its not worth it, there's next to no new content after you save cassie currently, at some point an update may be released adding content but currently there's not really much of anything, you can renovate the basement of safehouse which turns into a bdsm dungeon, you can put cassie in there, you can trap the bandit girl, there's pet play with the bandit, and a few other small things, but everything you can do with it can be done in a few minutes.