A kerosene heater should last a very long time and when the kerosene heater stops working it usually just requires replacing the wick that the kerosene saturates and is soaked up by.
An emergency kerosene heater has no electrical or moving parts and only requires sometimes replacing the wick so they can last as long as 30 years or more depending on how often you use the kerosene heater.
You can buy vented kerosene heaters that are safe to use while sleeping and vent to the outside and those should last 20 to 30 years as well.