What would happen to an organism if one of the organ systems were to disappear?

First of all it will affect the metabolism of the body. The organs will start to deteriorate since the processes are incomplete and eventually the person will die.

Answer: If the cells are injured or diseased, tissues will be affected and will not carry out its function accordingly. Since tissues are affected, the organ which is composed of tissues are also affected and it will not carry out its function properly then the organ system to where the diseased or injured organ belongs will also be affected. The organism will be affected and get sick and weak. If not treated, the organ system will shutdown and the other organ system will be affected and the organism will be die. Every part of our body somehow are connected to each other for the organism to live.