I'm gonna have to say no to your hypothetical. My reasoning? Think 'Doctor Who'. The main premise is that he is a time traveler able to
occasionally stop horrible things from happening. However, it's also understood ( in the series) that there are specific points/events in time that
HAVE TO take place.
Now, it sounds like you (or whoever) were able to 'time travel' into the future and see the events that were to take place because of this one
man's discoveries (and battle plan). The event described seems pretty catastrophic.
Given this information, I would say, no matter how horrible we may believe it is, it's gotta happen.
All this considering I'm going off of the reality that exists in a TV show (al beit a British one
Imagine what crazy stuff will have to happen to fill in the history that this guy already made. There will be a huge 7 year whole where this guy was
totally affecting everything around him. Now what?
Perhaps if he never invents the biological weapon, then no one dies, then the population becomes overwhelmingly out of control, then.... the world
implodes. I mean, shoot, how could you know?
It seems that large events are meant to happen to control other events.
What if by killing this one man you temporarily save a few billion people, but inevitably end up destroying the whole earth?
So, in conclusion, if I were a time traveler and able to change/help things, I would NOT attempt to fix any BIG events. Maybe something small here
and there.... like leaving a flower for someone who looks like they need it. Hopefully all that will change is a few exchanged smiles.