I don't really believe Christianity survived. Not really. The festivals are probably still there, but the religion, well. I doubt it. Got replaced in colonial times with what is already budding today. The Mollys being Catholic? Well, Mollies were workers, brought in from all over Bretonia, rather than settling there themselves. They were attracted by BMM offers of pay. And they were payed. They revolted because conditions were horrid, not because of any sort of religious intolerance. The idea that they're catholic...well, thats a rather crass joke, made to connect them to the IRA. They're not the IRA. They're not even Irish.
I just don't see the majority of Bretonians paying lip service to a religion, and I certainly don't see them earnestly following one.
They're Atheist, or Agnostic, or Deist, and they replaced 'religion' with nationalism. Loyalty to the Queen, a desire to make Bretonia a better House, Etc.