Question

If carnivores stop eating flesh or herbivores stop eating grass,what would happen?

Answer 1

It will disturb the food chain associated with us. It's a part of our ecosystem.

Answer 2

They will die. And the animals which eat them would die as well due to lack of food. It will start a chain reaction of events resulting in deaths of all species and overall population of Earth will decrease significantly, and will perhaps be termed as the 6th mass extinction.