When I worked at a university help desk (which was a while ago, but not nearly so long ago as what I'm about to say might suggest) the number of people who came in because the floppy disk they were using to store the only copy of their thesis or dissertation had stopped working was too damn high.
Also the first version of a new compiler (the one written in another language) is often skeletal, implementing only the features necessary to compile the full version (written in its own language), which is then immediately used to recompile itself.
That's the reason that only 15% of Crusader Kings II players have "The Marriage Game" achievement, which is awarded for getting married. In a game about dynastic politics.
It's not like the matter stops existing, it just stops being that specific element.
In the case of uranium, natural decay is mostly alpha radiation, meaning that 2 neutrons and two protons are ejected as a (high energy) helium nucleus, while the parent atom becomes thorium with an atomic weight four lower (e.g. U-238—>Th-234).
Other way around, actually: he started out making constructed languages for fun, realized that doing that properly required inventing the cultural and historical context in which it developed, and then, later, started writing fiction set in that world.
Actually less than that because only around 10% of the gold created this way (assuming a natural distribution of Hg isotopes) would be stable, so you'd get a bunch of β particles too. I don't even know how Au-201 would act, and it would comprise 30% of the output.
Ivanafterall smoke. Don't breathe this.