> What are the chances of anyone ever finding the discs, let alone understanding the instructions to reproduce them?
Pretty damn small. In 40000 years, it will come within 1.5 LY of another star. And then continue through interstellar space.
Though not strictly applicable to Voyager, for general context, you might find this analysis of the odds of coming close to a planet or star interesting: https://www.reddit.com/r/askscience/comments/2pe4oj/say_you_had_the_ability_to_fly_a_spacecraft_from_one_side_of_the_galaxy_to_the_other_in_a_straight_line_what_are_the_chances_that_you_run_into_something/cmvvytl