Both my previous nannies have gone on maternity leave and not come back! But nanny 3 will come back by mutual agreement with her child once s/he is born. Nanny says she will get bored at home with just a small baby and hardly need any maternity leave at all. I seem to remember small babies can be quite time consuming, actually, and think Nanny is a bit optimistic.
My Dc are both at school. One gets there and back under his own steam, the other could be taken there on the school bus. So in term time we could arrange Nanny to have quite short hours really, as long as she can collect DC2 at about 3.30pm each day. So she would collect a child and feed two, supervise homework. I can see that this might work.
Stupidly I forgot to ask the due date in the excitement of her her news, but I suppose if she took 3 months mat leave she would be on leave most of the summer holidays when XH and I go away. I could make use of holidays clubs and impose on my parents over the holidays - gulp. Even so neither of my DC slept through till they were 9 months old.
But your views on how long is long enough would be great. And did anyone have a nanny who came back from mat leave too soon?