Sickle-cell disease is inherited by the autosomal recessive pattern. It needs two defective genes to make the disease expressed. One gene will result in the sickle-cell trait, not the disease.
Assuming that the parent is homozygous dominant(normal) and homozygous recessive(has sickle cell disease), the offspring would be: 100% sickle-cell trait. It is not possible to have a sickle-cell disease and normal offspring.