[hexagonal]

Remember, it's got a 14 year lifetime because the half-life of Pu-241 is 14.1 years. At the end of that time, half of its mass will be gone, and it'll be producing half as much heat. It won't produce a steady 2KW for 14 years and then bing, go out like a lightbulb. Power produced will slowly fall over time.

[eru]

You mean, half of the plutonium mass will be gone. It will be almost completely be replaced by other elements. Though I don't know how much energy they give off in radiation, or whether they are stable.