Well there are two theories that I know of for this situation 1) he has been sent back in time because he was there before and now must fulfill some task to help the future become what it is/was. 2) he was thrown back in time by an accident and now every action he takes will have a positive or negative impact on the future to come creating a parallel universe. 

If 1 is true then he could make it so his model is never built and he would disappear. If 2 is true then it doesn't matter what he does because he is from a different time stream/universe.