The problem with her staying the UK, to set up a dance school or hairdressers, is her visa wouldn't be sponsored by the BBC anymore, this means if Joe wants to marry her and wants her to give up Strictly, I don't know how UK visas work, but I'm guessing it would need to be a fairly short engagement.
Same goes for pregnancy, as soon as she gets pregnant, she won't be able to dance professionally, so if she's not working how will she stay on a work visa?
That's if she wants to stay in the UK, her fan base is here yes, but it's clear she is very close to her family and misses them a lot. So maybe she won't actually want to stay in the UK, permanently.
There is also a chance she could do DWTS Australia next year. She couldn't do it this year cause of here comes the girls. But I would say she will easily get a spot on it, cause correct me if I'm wrong, but isn't Jason Gilkinson one of the directors of the Oz version. He is the one who spotted Dianne when she was 18, and has been looking out for her ever since, she is also under his management company. So If she does decide to do Strictly & DWTS, I don't know where that will leave her and Joe.