I was worried about the USB opening and water, so taped it up every time it was used. I can safely say that wasn't what broke the light. If I use it in the wet again I'll tape up both the USB and on/off switch. And maybe design it a small umbrella and matching wellies.
Moon Comet will die if it been directly exposed to water for a prolonged period of time (in this case, lack of mudguard).
They usually do have good sealant, but as @Netakure mentioned, the USB port is usually the main culprit.