What would happen to your ecosystem if the decomposers were removed?

Nothing. There is a misconception that there is an energetic cycle in an ecosystems but that is erroneous. There is a cycle in nitrogen and other nutrients that decomposers engender and, eventually, plants absorb but there is zero energy content in those as plants take 100 of the energy from the sun. The purport of decomposers is to return nutrients to the soil, not energy.

Energy only flows in one direction in the biological world starting and getting dispersed out by the different biological organisms until is thoroughly lost to the entropy in the universe. A decomposer is yet another organism that consumes the energy amassed by the plants from the sun and disperses it out.