What would happen if a disease killed off the top level of an ecosystem?

The trophic level beneath will flourished as it isn't hunted anymore. however, the trophic level beneath that one will die off as the increase of the one above, due to the extinction of the top level, will eat them off.

example. you have:
1. eagle
2. frog
3. cricket
4. plant

the eagles died off due to disease and the frogs increase as they are not hunted anymore. the crickets will decrease as there are more frogs to eat them up. 

Very hard to understand