If I put my computer in a safe and leave it for a few million years, when I take it out it won't have changed significantly in density.
If you put your computer in a safe and the very next day every person on this planet died, and there was nobody left to perform maintenance, the computer would not exist as an object in a few million years.
I'm assuming the safe is in your house, and the house is presumably made of wood, let's say. In a very short time the house would rot away, collapse and fall to the ground. The rain, wind, and sun light would eat away at the safe, meaning the safe would be becoming less dense, as the material from the safe would start deteriorating and occupying more volume than it originally did. More volume and the same mass means less dense!
Once the safe was destroyed and the computer was exposed, the computer would fall to the same fate as the house and the safe, destroyed by the elements of space, meaning the mass that once formed the computer "evaporated", or "decayed" into less dense matter.
There is no free ride, James. Mass is motion, and just like all mass in motion there is a cost to that motion. Motion is not perpetual. The natural progression of a given mass is for the mass to become less dense by means of expanding its volume. The ONLY other choices are for the mass to perpetually exist, or for the mass to become MORE dense over time, which requires either adding more mass or to compress the existing mass into a smaller volume. So take your pick, James? Which shall it be, more dense, the same, or less dense? The second law says it's less dense!
The second law of thermodynamics has never been wrong, and the second law says that an object has to become less dense over time!
The moon is but the earth expanding. The earth is but the sun expanding. The sun is but the galaxy expanding. The black hole is but.....
EVERY object in the infinite volume of space is expanding because there are no free rides. Motion occurs at a cost, and the cost is that the object has to expand to be in compliance with the second law of thermodynamics! We are but a spark flying away from a sparkler, on a large scale (earth flying away from the sun)!