>>3894768F.
How did it happen anyhow, did it hit something? A gust of wind? Downwards-facing sensor malfunction? I've read some horror stories about the first Mini suddenly deciding it's floating over an abyss and plunging itself into water.
Hope you've had the time to get some memorable footage with it, at least.
If it was recording at the time of submersion, I think the low-res version of the video should be still stored on your phone, accessible via the dji app. Hopefully it went out spectacularly, if nothing else.
