What happens to a baby if their skull does not fully develop over the soft spots a year after they are born?
When a baby is born, it actually has several soft spots all over the head - most are small enough though that they are virtually undetectable. "The" soft spot, the largest one right on top of the head, is the place where four bones of the skull come together. Typically, this soft spot does not close by a year old. Of course, every baby is different. Some appear closed as early as 9 months, others do not fully close until 2 years old.
Most likely, the hypothetical child in your question is developing completely normally. The main area for concern with the skull in baby and child development is in head growth. At every checkup for the first 2 years of a child's life, length, weight and head circumference are measured. This is to make sure the head is growing properly for brain development. It would be more of a concern if the soft spot closed very early and then the head was not growing at a normal rate.
As for your question - the year old baby who still has a soft spot is fine. In fact, both my girls still had their soft spots and almost no hair for the first year (one until 18 months) of their lives.