Not sure the 10-year mission would be a "failure", no matter what the outcome
Every one of these attempts has yielded us far more information about how to proceed in the future. If we are always afraid of failure we will still be bits of free-floating amino acids. I applaud the various nations and people/corporations that are willing to take these risks. Someday, way past our lifetimes, others will talk about standing on their shoulders.
At the kinds of speeds New Horizon’s probe is going, a small micrometeorite hit head on will utterly destroy it. A less serious impact with a smaller piece of matter could put it into a spin that would destroy any data-gathering capabilities the probe has, rendering its nearly 10-year mission a failure.
Needless to say Tuesday will be tense. But even if the probe is destroyed there would be one bright side, since the man who discovered the then planet might come to rest on it – or at least part of him.
Clyde Tombaugh, who discovered Pluto in 1930, is actually traveling on the New Horizons probe, or at least one ounce of his ashes are. He gave his blessing to the mission in the 1990s, and after his death the family released the ashes to be built into an inscribed container on the spacecraft.
Hopefully though, Tombaugh and the probe he enabled will carry on past Pluto and out into the Kuiper belt that encircles the Solar System. Once out there, New Horizons could still have a few more surprises left for us yet. ®