The pros that I should imagine will certainly be back are the Cliftons (all three - I think Joanne will be back partnering a celeb next series), Janette and Aljaz, the three newbies, and Pasha.
I'm less sure about Anton and Brendan, for different reasons. On paper they seem like 'certs', but this could be Anton's 'last hurrah' and Brendan's partnerships have felt like a bit of an afterthought post-Sophie. However, with Ola on her way out, that would mean the longest-serving pro would be from series six and even that isn't guaranteed.
Aliona, Natalie and Kristina are all at stages in their life where they may be considering starting families. Of the three of them, I'd say Aliona is the most likely to be back as she's a bit younger and there is the possibility she could be the first professional to win twice. Having read the comments about Kristina possibly doing the reality rounds, it seems like she may want to cut her losses. Natalie, meanwhile, seems resoundingly slotted into duffer territory now and with her own tour with Ian next year, she may feel it's time to move on.
The only pro I really don't expect to be back in Tristan, and I would be very disappointed if my hunch proves to be correct as I think we saw an improvement in Jamelia and he's been brilliant on ITT. With the male line up having so many 'keepers' though, I'm not sure he'll make the cut with the male pros cut to seven on the back of being in the dance off for all but three rounds in his first two series.