What will happen when everyone dies?

Depends on what you believe...

-Since no human is breathing anymore, the Carbon di-oxide cycle will be affected.
-Most of the machines which were being used by humans won’t be running anymore thereby saving lots of trees and energy.
-There will be a lot of accidents after a few seconds of death (for example: planes crash landing because pilot is dead, power stations will run out of fuel and it will become useless)
-There will be a rise in the amount of Methane, Ammonia and Hydrogen sulfide in the atmosphere due to the gases emitted by the decaying bodies.
-Insect and scavenger population will increase tremendously because they have a lot of food available now
-Insects on your body will become extinct after a certain period of time.
-Buildings and other man-made structures will wither away.
-Due to the increase in oxygen availability (oxidation will become quite faster) and no maintenance of steel structures, all metal structures will be reduced to rust in a few hundred years.
-Species whom we had almost reduced to extinction will restore their population.
-Soil fertility would increase after a few years of human extinction.
-Pet owners will have their pet dog sitting next to their corpse.
-there will be no more pizzas
-nature will restore itself to its (almost) original form.