To go on maternity leave (and take the full amount) knowing full well you won't be going back without telling work until you have to give notice before you're supposed to be returning?
This is what I am doing at the moment, mid way through my maternity leave and I do not intend to return but won't be informing work until I legally have to.
My main reason for this is to safeguard myself in case the situation changes, I think it's far more sensible, even if you think you won't be returning, to not actually make it known until the end.