Plutonium 238 has a half-life of 87 years. The power output of the thermocouples has fallen over the years so V1 doesn’t generate enough wattage to operate all the instruments at once so they shut down all but a few. And you are correct, there will probably be a failure on a critical component before the power runs out.
My error as I was looking at the wrong isotope. Much thanks for the correction. That is what I like about Free Republic. Our errors are immediately pointed out by other posters. This does not happen in the main stream media also known as propaganda central.