Ok, so we just saw the episode, time to recap:

In general, this was a pretty emotional and developmental episodes, we learned FP's backstory and we see a lot of her character and how she copes with this situation.

We learn exactly how she got locked up, which is revealed to be completely on her fathers note, we see her befriend CB. And for the biggest turn in the plot, she overthrows her father and rules the Fire Kingdom, in an attempt to be a far gooder ruler than her father ever was, right down to wearing similar clothing and locking him up. And Finn and FP do not get back together, but they're glad that they can be close friends for now.

Even though this seemed to tie up the story arc, I don't think this is going to be the ending of FP's story, we still have a lot to see from her and I feel that having her take control of the whole Kingdom would be a bit of a demotion to her character, since we wouldn't be able to explore much from her anymore.

In total, it was a pretty good episode, very sad and emotional, and I believe it will carry on to further plots.