Can schizo-affective disorder develop to schizophrenia?

Not really: By definition, one either has one condition or the other. Practically speaking, treatments for both conditions may be rather similar. Schizoaffective d/o is when a person has a major mood component to his or her illness plus had psychotic episodes during times when there is no mood disturbance.

No: Technically the diagnoses are mutually exclusive. In schizophrenia, symptoms of psychosis would be much more prevalent as compared to the mood symptoms. Whereas in schizoaffective disorder neither the mood symptoms or the psychosis predominate. Frequently though people can at one time or other be diagnosed as either, because the diagnosis is only as good as the history available at that time.