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.