Question

What would happen if a keystone species is removed from an ecosystem

Answer 1

the whole ecosystem would be disrupted and it would die out because one animal in the chain is left without food so that animal would die and the animal that consumes the dying animal would then die out.

Answer 2

The ecosystem would be greatly effected, most likely causing the system to fail, and could lead to the death of a species, or a very large population boost, or even worse.