Normally this makes sense, because you're asking why money was wasted. But, in this case if it's permanently bricked you will actually save money, because if Voyager 2 is bricked the team working on it is now redundant. It's not like they had an incentive to be incompetent and waste money - very much the opposite.
You calculation only makes sense if you put zero value on operating a probe that far out in the galaxy - in which case you should be asking why there was a team working on it in the first place.
But that value is not zero, and replacing it costs quite a bit - both money and time. Asking how and why this happened is a valid inquiry.
Under the assumption that it is bricked, the value is indeed now zero.
I think where we differ is that you are assuming it will be replaced, but I don't think it will be. It's way past its design life so it was going to expire at some point.
For science, I would want to do an enquiry anyway - I'm just commenting on the financial/accountability aspect.
