Low battery looks the same as with the red light slow flashing as after you crash. A semi slow blink. It initiates a little before the battery is too depleted to maintain flight, say 30 seconds or so, before you need to be on the ground. If you ignore the change in blinking speed and keep flying the copter will initiate a very fast descent, generally level but with some directional instability, that increases in throttle or directional control will not compensate for. In short, you're going down.
I don't think you can over discharge the battery using the low battery level descent point in the Ominus. Once the battery is too low you won't get the fast flashing light if you plug in immediately after setting down/ It is possible to take off again on a low battery if you wait a few minutes for the battery to cool and voltage to creep back up. You won't be in the air long before it heads for the ground with virtually no advance warning though.