Seems far more likely that in 40k years, humans will have discovered the ability of interstellar travel. Heck, at that point we could go out and fetch Voyager 1 ourselves before it comes within 1.6 light years of AC+79 3888. If we can't in 40k years, it's likely not possible that we'll ever leave this solar system. It could be that's it's just not physically possible. But more likely, do we survive long enough to develop that technology?

I've always viewed the Golden Record as a way to make humanity feel better about its future. The need to leave a legacy behind is core to who we are, and that's exactly what we did with those two discs. We left something behind that will survive for 1 billion years, with the infinitesimally small hopes that someone will find it. But, it makes us feel good.