In 12 Monkeys (1995), at the end of the movie, Cole is killed by a man in the airport. So did sending Cole into the past for a cure work or not?
The ending of 12 Monkeys implies heavily that they could not change time. By sending Cole back in time, they completed a circle. It's a predestination paradox.
Cole changed nothing. If anything, he allowed it to happen as history said it happened.
Cole did as best he could given the information and minimal help provided.