In parallel to your event task create a timer task as well, set the timer to 30 min. Connect the timer and event task to a decision task. Open decision task and chose Treat the input links as: 'OR'. And set the condition in decision task as Event.wait.Status=Succeeded.
After 30 min the timer will succeed and it will go through the decision task and then you can decide how the flow goes from there.
P.S: I know this is an old question, but someone else might benefit from it.