Embryos can be frozen if there are excess embryos. They are transferred (FET) later months according to cycle.
In cases if pregnancy does not occur due to failure of implantation or poor embryo quality, doctors will counsel to provide further options
and to clarify your doubts.
Depends on quality of egg and sperm and physicians skill also plays a part. Generally we have 60% success in young healthy couple, 30% success in aged (more than 35 years)