It is often claimed that the B-52s are already decades old and won't be airworthy for long. However, the B-52s built first are not the ones still flying, and replaced components have made the airframes flyable for years to come. In fact, at average usage rates, current B-52s could last for the next forty years. Beyond the lack of a requirement, the Department cannot afford further purchases of B-2 aircraft or funding to support actions that could contribute to that end, such as annual industrial base funding. Not for at least four decades.
Aircraft often have their lifespans extended through refurbishing programs.
I would be surprised if there's an original rivet in any of those airplanes we have out on the ramp. It's been rewinged. It's been reskinned. It's been retailed. It's not an unsafe airplane.