Every other monument we have yet made lies within the solar system. The voyager probes are humanity's first physical journey beyond our home. It's human curiousity reaching out into the cosmos for the first time. As cosmic infants walking outdoors for the first time. Even if we eventually pass them some day, they were still the first.
And even more, there are plaques on them waiting for that 1 in a trillion chance to be found by a distant alien race. Long after humanity goes extinct those plaques will endure. Even if we can see the beginning of the universe with telescopes, those telescopes are near to our planet.
The voyager probes could potentially exist in the future as the only thing outside of our solar system to prove we ever even existed....hell depending on how and when we go out, they might be the only things anywhere
edit: I forgot about pioneer. pioneer 10 and 11 were launched first but voyager 1 and 2 left the solar system first. Also there is new horizons. 5 probes total.
Sorry to be that guy, but Pioneer 10 and 11 were the first. They stopped communicating in the early 2000s though, so the Voyagers are the only ones still providing scientific data about the heliosphere.
Perhaps we can find solace in the fact that Voyager will stand as a monument to our determination for scientific progress, space exploration and technical ingenuity.
The probably of Voyager crashing into anything is so incredibly miniscule that it will very likely outlast our civilization and even us as a species. Any deterioration of the physical craft in a vacuum will be so slow it will last for geological timescales.
How long does it take to actually transit/communicate with it via s-band or x-band? It's more than 15 billion miles away, it's pretty crazy to think about