There were reports that all the pros had their contracts renewed or were going to but that hasn’t been officially confirmed.
Kevin Clifton, a well known dancer, popular with many left for a year and the BBC won’t have him back. I think you’re overestimating how loyal the BBC will be to the dancers, they are replaceable and once they go they don’t come back. Also there’s no guarantee she’d physically be able to get to the level required to continue dancing. That’s before you consider the practicalities of raising a child while working 6 and a half days a week for a few months, 12 hour days.
I don't know, maybe. But Kevin was different though. He completely left with no intention of returning, then only wanted to come crawling back after covid ruined his tour plans and he had an unsuccessful year. Not quite the same as taking a planned year of absence to have a child.
As for the practicalities, she's not a single parent. Raising a child would be a two person job between them. Not quite the same, but Gorka went the whole last season without seeing Mia so it's not like other parents on the show haven't made sacrifices during the season's run. During a normal season she'd at least still be able to see the kid when she can.
Anyway, I don't think they'll be getting pregnant for a few years anyway so it probably won't even be an issue. They probably won't even start trying until after she's left so the issue is practically non existent imo.