No, most of the Chernobyl deaths were not due to iodine uptake in the thyroid. Thyroid cancer from iodine updtake is rarely life-threatening.
Higher cancer risk continues after Chernobyl;
NIH study finds that thyroid cancer risk for those who were children and adolescents when exposed to fallout has not yet begun to decline
Nearly 25 years after the accident at the Chernobyl nuclear power plant in Ukraine, exposure to radioactive iodine-131(I-131, a radioactive isotope) from fallout may be responsible for thyroid cancers that are still occurring among people who lived in the Chernobyl area and were children or adolescents at the time of the accident, researchers say.
http://www.cancer.gov/newscenter/newsfromnci/2011/ChernobylRadiation