Ironically, I think the Sovieshu time travel side story/au is the best ending for Rashta.
I'd love a world where she escaped, never met Sovieshu, and went on to live a happy and free life, but that was always unlikely. She had no identifying papers. She couldn't read or write, which would give away her status. It would have been hard to find a way to support herself and stay under the radar.
In the time travel au, it leaves off with the idea that after Rashta gives birth, she'll be sent to a separate villa. True, she's heartbroken Sovieshu doesn't love her, but he never truly did. Better for him to be honest.
But she won't need to worry about Lotteshu. Sovieshu is keeping her from Ergi. She won't have much political power, but she'll live a life of comfort and wealth without needing to work for it. Since Glorym won't be declared a princess, she'll be left out of many plots and intrigues.
Sovieshu will probably be keeping an eye on her, but I doubt he'll micromanage her actions the way he would if she were still his mistress or an empress.