Fly it. Keep it in sight and have fun. RTH and cancel buttons will work and you have battery strength, speed, distance, and height readouts on the RC. Everyone should feel confident flying without a phone/tablet because if you have not had the app crash or device die, you will. Think of it as practice for when it happens.
What happens if app dies and you only have RC working...and you for good reason have to now change your RTH point or else you will not have enough power to go back to the original RTH point? if it crashes or gets lost are you SOL b/c DJI will not warranty the damage b/c they don't care if their software works...I've read that they officially do NOT warranty their software...!!