The matter that gets pushed beyond the observable universe due to cosmic expansion is not considered "destroyed" in the sense of being annihilated or ceasing to exist. Instead, it is simply moving away from us at speeds greater than the speed of light, as a result of the expansion of space itself.
The observable universe is the portion of the universe that we can currently observe or detect because light or other signals from those regions have had enough time to reach us since the Big Bang. However, there is likely much more to the universe beyond the limits of what we can observe.
The expansion of the universe means that the space between galaxies is stretching, causing them to move apart from each other. The rate of expansion is such that there are regions of the universe that are already moving away from us faster than the speed of light, making it impossible for any light or information to reach us from those regions.
While we cannot directly observe or interact with matter beyond the observable universe, it is still expected to exist. It's important to note that the conservation of matter and energy is a fundamental principle in physics, which states that matter and energy cannot be created or destroyed, only transformed or redistributed. Therefore, matter pushed beyond the observable universe due to expansion is still expected to exist in some form, even though we may not be able to observe or interact with it.