I'd take maternity leave. Leave your options open. You don't know what the next 12+ months are going to bring and having a job to go back to might end up being a godsend. I wouldn't burn your bridges if I were you.

I have two girlfriends who were in the same situation, swore they weren't going back to their old jobs, but life and circumstances get in the way and both of them ended up going back and were grateful they had that option. Doesn't mean you have to stay if you go back, but it's just a safety net.

If you don't go back, you don't go back, but no need to tell them that now.