What might happen if the population of producers in this ecosystem died off. explain?

If the population dies off then the consumer will die off as well. 

Best I wouldn't say all the consumers would die off, because not all of the producers died off, they just significantly decreased. This would also lead to a very significant decrease in the consumers, and would lead to increased competition between different consumers due to constraints on resources. So in addition to there being less consumers in the ecosystem, there would be less diversity in the ecosystem as some species would likely die off. Through natural selection, the consumers who are left would adapt to the new environment. For example, consumers who are smaller and burn less calories may be more likely to survive than consumers who are larger and burn more calories, so future generations may tend to get smaller and smaller. Whoever is up next on the food chain is affected in the same way. However, what really happens in the long run depends on why the producers significantly decreased. If it was because of a climate change, the producers' numbers may fall in the short run but go back up again in the long run as they adapt to the new environment or are replaced by other producers more fit for the new environment. Then the consumers may have to adapt to the new producers in the environment. As you can see, sometimes nature can be quite unpredictable.