What happens? Nothing, usually.
As you have probably noticed, treasures and gold tend to be quite common in not-so-easily-accessible (or outright improbable) places in R3 (for example, check the blades of the Calador windmill as well), so after a while things like Dagobert Duck carrying a hundred gold pieces on it aren't even that surprising anymore.
IIRC there should also be a grave with the name Big Timmy (~) on it somewhere nearby (although I don't know whether that's the case in all language versions of the game).
For example, there is also a duck called Dagobert (easter egg spoiler
) on Caldera. ;)
* Calador, not Caldera, of course.
Well, they're both on the mainland. :) I actually didn't notice and read it as Calador until the correction.
Makes one wonder where the name Dagobert came from. I don't know if it is known worldwide, but in the USA, there is a comic strip called Dilbert that parodies Microsoft. Some of the characters? Dogbert, Ratbert, etc. I wonder if that was the inspiration.