> I heard once it will eventually lose it's form entirely

It will be sitting at something like -450F. Could it really lose form!? Is the idea that all the phonons could converge to one point, shifting an atom of metal (which will happen infinitely with infinite time)? Maybe with random photons/hydrogen/whatever "continuously" adding energy?

Neat.

From what I recall, one of the hazards of long term space travel is that nearly any material will start sublimating atoms in the hard vacuum of space, with things like cosmic rays adding to the woes. Some over time it will start deteriorating.

Not sure about “melting” into an amorphous mass, I guess in theory the probes gravity could do that, but I would imagine even the tiniest force would disturb that and dissipate it.

One issue is that over long enough timeframes, even atoms that we consider stable will decay - particularly ones that are heavier than iron, which will decay towards iron or nickel. That decay will eventually compromise the structure of the probes.