Currently the event editor cannot be configured to execute a certain behavior only if a certain condition is met(if external service has a response in your case). What you may want to do is, let the refresh happen anyway. configure conditional layouts on your section based on a response property that is set/reset through your activity. If there is a response, show one layout versus showing another with a message when there is none.
If there is a gap in my understanding of your requirement, let me know.