En-ROADS does not currently include a way to simulate negative economic growth (degrowth). We may add it in some sort of way in the future. Keep in mind, however, that En-ROADS is a global simulator, so it covers all levels of economic development across countries.
Many people talk about the path to addressing climate change as one in which emissions and economic growth are decoupled, since currently greenhouse gas emissions have risen with increases in economic growth over the last century. With a transition to renewable energy and energy efficiency, there is hope that we can continue to lift people out of poverty and develop economically without the greenhouse gas contributions that this has historically entailed. There is vigorous debate on this issue (example here).