A simple yet very powerful integration between Chatfuel and Dialogflow is the ability for Dialogflow to respond back with a custom payload that trigger another flow in Chatfuel.
This also carry on all the variables from the conversation so you can follow-up and make action.
As described here:
This is a very very powerful features since many business logic can be taken care of in Dialogflow and could be send back to Flow XO.
Right now the only way to achieve this is by creating quite complex flow where response path are save and then custom HTTP trigger are created between Dialogflow fulfillment process and Flow XO.
Since this is not at all the goal of Dialogflow fulfillment logic, it's basically a hack that is complex to support.
The custom payload in Dialogflow is exactly for this purpose and should be process by Flow XO.