In the sequel, Time After Time, which maybe wasn’t out when this thread started:
A time traveler in the past when the hero does this comes back to find no project. He meets up with others who vaguely remember it, and then goes back to prevent the hero from stopping the meeting of the parents of the guy who invented time travel, so all is restored.
One big problem with time travel stories where the past is changed is a failure of nerve. For instance, in this book there is leakage from a timeline where WW I never happens, and where JFK ran in 1964. But if WW I didn’t happen WW II wouldn’t happen, JFK’s older brother Joe would have survived, and even if JFK had been born, Joe would have been groomed for the presidency, not Jack.