Question

What would happen if there were no decomposers in a food web.

Answer 1

There would be dead animals overloading the Earth. Think about it, without worms and other things that break down dead things they would still be here and just sit there. 

Answer 2

If there were no decomposers in the food web, the whole entire food web would be destroyed in a sense. Decomposers break down animals remains and turn this into nutrients which is then used by plants. Plants grow and provide energy to herbivores, herbivores/mammals provide energy to carnivores, and then fecal/animal carcasses(remains) supply the decomposers with something to decompose. Without decomposers, there would be no food web. Hope this helps!