What if all the bacteria suddenly died off?

The earth would be a lot more smelly because there is less recycling of dead animals and plants. There will also be less nutrients available to plants and animals. We would also have a more difficult time digesting our food because there will not be beneficial bacteria in our gut to help us digest food. Cows would be in trouble because they need bacteria to break down the cell walls of the plants they eat.

We'd die is the short answer.  Our bodies are dependent on 'good' bacteria.

ALL of it?? Bad news included no longer being able to digest our food, bodies never decomposing, etc.