yes keeping your nanny is a finanical comittment when you are on ML but the pros outweight the cons imo
having extra pair of hands for no 1 and no 2, will be worth their weight in gold (and cash)
nanny can have baby while you can sepnd some time with older siblings, so that they dont feel pushed out, you can also rest, giving birth is knackeringm let alone having 2 more other children to consider
losing their nanny, and having new baby can sometimes be a bit too much for some children, esp if then you are going back to work and getting another nanny
I have had 3 mbs on ml and all have kept me on on full pay and less hours (ie finishing hr earlier etc) I personally wouldnt stay working for someone who basically told me to go away, yet come back in 3mths time (even though you are paying a retainer) but thats just me
3mths work is hard to find, so your nanny may decide to find a new job but on other hand she may agree to what you are suggesting
it depends on the nanny, i wouldnt, but have known friends to leave, find horrible temp jobs, hate every minute of it, and then go back to family
have a chat to your nanny, and see what she says/thinks