This is a huge debate in the scientific community, whether it is possible for entropy to be permanently reduced. The short answer is "with what we know, no." The problem is that our understanding of the universe itself is incredibly inadequate to be able to answer the question with any certainty. The oscillating universe theory states that eventually entropy will actively reverse itself.
It isn't hanging on to scientific fantasy; it is merely acknowledging that our picture of the universe is incomplete, and it is foolish to say "the universe will absolutely hit max entropy and experience heat death, and nothing will ever change that". With our current understanding of the universe, will it probably experience heat death? Yes. Do we know for a certain that this is the only possible ending? Absolutely not.
In reference to the diamond thing, that is essentially based on the idea that, given an infinite span of time, every single outcome with a non-zero chance of happening will happen, without exception. Think of it like this: If there is a 10% chance of something happening in a year, then given 10 years, it will most likely occur. If there is a 1% chance, then given 100 years it will mostly likely occur, and given 1000 years, it will almost definitely occur, etc. Following that, if there is even the slightest chance, maybe 1 x 10^(-10000)% in a year, given an infinitely long time it will eventually happen.