See, it’s a good question! I looked it up, but didn’t find a firm answer. As far as I could figure, they:

• eventually freeze, crack open, and thaw
• get stepped on by a heavy animal (they are eaten by ducks & beavers)
• clunking around the bottom of a river/pond, letting the sand wear it down.

All conjecture, but I don’t know!

I mean, moving the whole solar system just makes sense at a certain level of energy expenditure - if you are already generating enough power to do interstellar travel, might as well take the whole house with you. Sucks if you live here and don’t like the new travel direction of the system though, I guess. Find a new solar system to live in at that point?

apprentice tall