Baby with minor sagittal craniosynostosis (scaphocephaly) and the doctor is saying it's fine and no surgery needed? Why not? What will happen?

Hopefully nothing ! Sagittal bones are not the skull bones that grow to allow normal head growth, they are mostly due to coronal and lambdoidal bone growth. Scaphocephaly is usually not associated with syndromes. It occurs frequently in premature infants, and comprises 50 % of all abnormal head shapes. Nothing serious should happen, make sure you follow this with your doctor.
Scaphocephaly. the skull in infant has a sagital suture stenosis gives scaphocephaly and a suture exactly perpendicular-coronal suture apart from that there are additional suture which allow the head to grow as long as the soft spot is open and the head is growing you have nothing to worry except slightly different looking head.