Oh what a shame. Just having an idyllic day out at the seaside. What could possibly go wrong? And then your pannier just clips a post and throws you over the edge. I feel so sorry for him.
If you ride motorcycles, as sure as eggs are eggs, one day you are going to drop it but nobody expects to drop it that far!
Reminds me of a spill a former buddy of mine took in the UK in the 70's. He was riding, slowly, in dense fog (vis. approx. 20 ft) when he noticed a pair of flashing amber beacons just before they went past on either side of him. He hit the brakes but too late. The next thing he remembered was coming around in the ambulance on the way to the hospital. Turns out he'd found a set of roadworks where the local council was laying new main sewer pipes (the big concrete ones about 6ft across). The hole was 12-15 ft deep and he went straight to the bottom (the hole had vertical sides/ends). His Triumph Daytona had the front forks sheared off just below the bottom stanchion and he picked up a couple of broken legs and three cracked ribs!