What would happen if all the decomposers on Earth died?

There is theoretical examples. Planets that are distant in the radio scopes show that lowest bacterials cannot sustain oxygen based life. Although some types of water fungi do produce breathable frog mix. The planets themselves are started at the biokryptic level when shell animals like worms, or mites dies and become the first vegatative earth soils. The major cycles following are not inhabitable during the hot volcanic periods or reactions. These minerals are time releases from similarities to distant living planets that make the shape and information needed to sustain domestic, mammal,tropic, and sea life. Finally birds evolve from the first stages of attempted sea life. On a theoretic planet that lost 90% of the active bactrium decay the people would grow larger like dinosaurs and would mutate towards mermaids, and alligators to hide their eggs. This is called shape morphing and happens because it is data prone. The planet must have at least 7% of bacteria to produce air. http://www.planetsystem.com

They probably wont so i wont worry about it.But if u insist i think that all humanity will die gradually.

dont worry, its not going to happen, but to answer you're question, we would for sure die, insects & small animals are what keep this earth going, if none, life would not exist, but only a major event would cause that, such as alien invaders or meteors, or probably global warming, maybe kitty cats.

We'd be up to our butts in dead stuff and the soil would soon be depleted since nourishment could not get back into it.

All life would cease to exsist if all the bacteria and microflora dissappeared overnight. all of the biomass would get tied up in dead organisms and our whole food web would fall apart

we would be overcome in disease and pestilance and would die as well