I believe that if a complex ecosystem of non-sentient biota were to be obliterated, then something of value would be lost irrespective of whether there is a human being or a sentient being to observe it. Nature and the world has some intrinsic value in of itself. There may be different degrees of values and depending on who is judging, there could be additional criterions on top of the intrinsic value. However, any object having an intrinsic value means that ultimately it is part of the universe and has merit irrespective of anything else. In other words, a Kantian would treat such a thing as an end in itself. For this reason, something of value will be lost if this complex biological system were to be destroyed.
An opponent of this view could say that because there are no humans to observe it, there is no value in it. However, this objection is ultimately false. Suppose that there was a choice of whether to have a mountain like Everest on this planet. Surely, the opponent would say that if Everest did not exist then the world would lose something of value. And this judgement is true whether or not human beings actually know of Everest.