Reporters and Editors write their own obits and update them (usually) yearly. They are kept on file "in case."
Obits of celebrities, public persons, et.al. are written in advance and updated as needed.
My obituary is written and on a floppy!
By the way - one thing obit writers are told right away is that nobody dies "unexpectedly." Suddenly, Without warning. whatever ... but never unexpectedly.