I'd agree with the others - take your leave, state your intention to return after a year... then you can change your mind.

Working part-time for someone else during maternity leave is perfectly fine, I do know some people who have done this. However, only after their SMP has stopped being paid, as otherwise they'd lose their SMP.

I don't think they have to give you part-time work, but I believe that in Australia they have to prove why they didn't give it to you. I know in the UK they're not forced to at all, although most places will look into it.