I would like to see cartridges designed ecologically - refillable perhaps, or at least designed to flow as much out as possible - and allowing you to override the "toner low" warning and keep printing even if it's almost dry.
However, the internals of the cartridge will break down over time. Typically it's the "blade" that evens out the powdered toner that wears out, leaving too much toner stuck to the page and results in those gray-page prints and streaks/lines.
If you buy refilled cartridges, the blade seems to be the most common failure point long before you run out of toner.