They disappear when their destination is re-developed, this applies to both passengers and goods; the game treats them in the same way!
Passengers disappear when their destination is redeveloped in your towns. Goods have destinations in commercial building, if they are redeveloped the goods disappear.
Basic commodities oil, ore, coal and timber have destinations in processing plants, as these are never redeveloped they should never disappear. I have never noticed these disappearing!
- This reply was modified 7 years, 2 months ago by Norfolk_Chris.