The sad news broke tonight : Neil Armstrong, the first human to ever walk another world, died today. We lost him forever. He died before we could defeat death.
Once again the horror of death strikes. This time, in addition from wiping from us forever a hero of humanity, he wiped from us forever a memory that will never exist again. Never again will a human being be able to experience being the first to walk another world. That beautiful experience is lost forever too, along with all the memories, dreams, desires and wishes that made Neil Armstrong.
But thanks to him, humanity made a giant leap. We'll fill the stars and conquer death. The spark of intelligence and sentience will not extinguish. That's the best we can do to honour him.
Source : http://www.reuters.com/article/2012/08/25/us-usa-neilarmstrong-idUSBRE87O0B020120825
He was not responsible. He participated.
Doesn't follow, existential disaster seems likely.
Honoring Neil Armstrong isn't anywhere near the top of the list of reasons to avoid an existential disaster. Hence it's incorrect to say that we would be doing that to honor him.
(Experience is a physical phenomenon that can be (re)created, although in this case it would have to involve false beliefs. That would still hold even if Armstrong never died.)
One person that may have actually played a non-replaceable role was Hal Laning; according to that article he wrote some particularly tricky code that turned out to be critical for the mission.