There would be much less destruction to the Earth. This is one of the negative effects of plate tectonics at work on the Earth.
Volcanoes can clearly cause much damage and destruction, but on the flip side, economically, they also have benefited people. Over thousands to millions of years, the physical breakdown and chemical weathering of volcanic rocks have formed some of the most fertile soils on Earth eg. the rice-growing regions near active volcanoes in Indonesia. Thus, the agricultural economy of a world without plate tectonics would be affected as there are fewer suitable areas for cultivation of crops.
Living in a world without plate tectonics also means losing another source of energy, geothermal heat from volcanoes. Geothermal heat can be used to run turbines to generate electricity. Thus, the price of oil will escalade as the demand for oil increases.
Without the mountainous terrain formed by the plates movement, we can expect climatic changes. Now, there are two basic effects on precipitation caused by mountains. On the windward side, there is a greater amount of rainfall and on the leeward side, a significantly reduced amount of it.
So the short summary is death rates will decrease, however, there will also be economic losses.
