If people in other countries stopped using as much oil as they do today, the most accurate statement regarding the impact on the economies of Saudi Arabia and Iraq would be:
Their economies would suffer as other countries bought less oil that Saudi Arabia and Iraq produce.
Both Saudi Arabia and Iraq rely heavily on oil exports for their national revenues. A significant decrease in global oil demand would lead to a decline in oil prices, thereby reducing their profits and economic stability. Although there may be some short-term adjustments or attempts to diversify, the immediate effect would be a substantial negative impact on their economies due to decreased oil sales.