Katya was a really high performing competitor in the ballroom/latin world so she could return to that. Maybe not competing but judging, teaching etc. I don't think she'd get much TV work post Strictly but she could probably continue her career in dance.
She's already had Ed & Mike - if she doesn't want to turn into the female Anton, then that's another reason to leave. If there's anyone who should get the older MP type next year, it's Amy after a 4 series run of Danny JJ, Karim, JJ & Tom, 3 of whom were contenders on paper and the other seemed to have voting appeal despite weak dancing.