What are the community's suggestions on incorporating open-domain models?

Suppose I have a specific task-oriented model trained with the data that I have specific for my task, and RASA’s inbuilt intent-entity classification and dialogue state engine takes care of all of this, but I also want to have an open-domain model (like, BlenderBot) that picks up on the conversation when the user is not talking about the tasks my chatbot is built for?

I know that we can handle this case using conversations and mention that the chatbot cannot help them with this, but I wanted to know if someone has tried out this approach mentioned in the first paragraph and whether they have been successful with it.