It varies but this is the best answer I found.
"When her mother's heart stopped, her inutero
child does not die instantly. Instead, the inutero
baby dies slower. When the mother's heart stops
beating, the baby begins to suffocate for lack of
oxygen. The baby can feel. The baby is in pain. At 4
minutes, the baby begins to suffer severe
neurological damage. The process gets worse.
Baby would have finally died 15 minutes
after her mother had been killed."
then there is this
It depends on the gestational age of the fetus. If the fetus is 27 weeks or later an emergency delivery of the baby can be done to try and save it. A baby could survive earlier than 27 weeks. With each week survival rates increase.
Otherwise, the fetus will die along with the mother because her body is what is keeping the fetus alive.
Read more: http://wiki.answers.com/Q/What_happens_t...
If the mother was actually dead then the baby would die too. For example if she died before medical help was available, th ebaby would most likely be dead too. Recently in the news was a story about a woman who kept on life support machines so her baby could be born. The baby was born two days after she was pronounced brain dead. They turned the machines off after the baby was born. I think the longest a woman has been dead but on life support to keep her baby alive was 3 months.
all are possible