There is conservation, not just of fairness, but of value in general.
In any closed causal system, this must be so. You can’t increase the amount of value that a given state of affairs is capable in principle of expressing throughout its whole future, absent any exogenous inputs of value thereto.
All that you can do is rearrange the value that is already implicit in it. And all such rearrangements use up a bit of the store of available value, dispersing it in such a way that, spread about indiscriminably, it can no longer exert any allure toward a particular terminus ad quem, or therefore motivate any work, any action theretoward.
But note that for any given moment in a causal order, the amount of value that it can express over its whole history may vary, depending on the decisions made in and as that moment.
There is for a cosmos at its beginning an optimum amount of value that it can possibly realize over its history, provided it follows the optimum pathway forward from that beginning, without error.
If it should ever err, then cosmic history would fall from its optimum path, and would forever thenceforth find itself unable to climb back thereto – again, absent any exogenous inputs.
The value that a given causal order can express – can actualize – is quite path-dependent.
Once a cosmos has fallen a little bit, and cannot climb back up, it can of course fall still further. And, again, absent exogenous rescue, that is what must sooner or later eventually happen. For, once infect a world with error, and that error never thereafter goes away. It leaves its mark permanently in history, and queers everything after.
To see this, think of a bowling alley where the distance to the pins is, like, 15 miles. The tiniest error at the beginning of a ball’s journey is going to land it in the gutter, sooner or later. No ball will ever reach the pins.
But even without exogenous rescue, a world may devolve to the general death of heat, and all other values, more quickly, or more slowly, again depending on the path it takes. The bowling ball may land in the gutter almost the moment it is released, or it may roll along beautifully for quite a while. In the latter case, more beauties will be realized than in the former.
So, while there is no way to prevent the eventual utter exhaustion of all the available store of potential creaturely value present in the cosmos at its inception, that process of exhaustion may actualize more beauty, or less. The world is eventually doomed; in the meantime, it may be better, or worse.
From the extensive comments added by Kristor to: