Simo 37, no you won't crash because the app crashed. When mine did it the first time, I nearly choked! Then I looked up and my Phantom was just hovering there waiting for its next command. They are very stable and the app just lets you see the video download and a lot of other stuff but the Remote Controller (RC) unit with the joysticks actually does the controlling. You can fire up your drone and take if off just like a "normal" RC airplane, with no screen to watch. You can control all functions from the RC in hand without any app running. However, you really should invest the $23 in Litchi and see what it can do. I love it and have flown with it since November when I last tried to upgrade DJI GO. I got tired of it crashing and felt like there had to be a better solution. I'm very glad I tried Litchi.
Good luck!
Jim
WA5TEF