You are absolutely right that Gefitinib is used for Non Small Cell Lung Cancer. I do not know what made your treating oncologist prescribe the drug for your father, but there is only one case report in the literature about the use of Gefitinib in Small Cell Lung Cancer. I am providing you with the link to view this article below:
http://annonc.oxfordjournals.org/cgi/content/full/17/6/1028
I think since your father had a limited stage SCLC with SVC obstruction and responded well to the first line chemotherapy, he should have been evaluated for a response after completion of chemotherapy. If he had a complete response he should have been subjected to a radical radiotherapy to the chest and a prophylactic cranial irradiation at that point in time. We should not have waited for his disease to come back and then resort to palliative radiation.
It is difficult to comment upon the survival of the patient without evaluating his current disease status.