There are many species that, without human interference, would be extinct today. Humans are not just a scourge for many life-forms, we are also the saviours.
There are various cereal crops that require human assistance in their reproduction. There are genetic bottlenecks present in some species of plant life that make them susceptible to disease. There are also a whole host of animal species that human intervention prevented their extinction. The Panamanian Golden Project frog was almost wiped out by disease, and many domestic animals only exist today because of their usefulness to humans. Without humans, these species would not be here today. Our extinction would mean the extinction of all of these animals too. That would make the incident a tragedy.
In the last 500 years alone, humans have been responsible for the extinction of 322 birds, mammals and reptiles. The human preservation of a handful of animals and plants does not nearly equate to these lost species. Humans are a net negative impact on the world. Therefore, their extinction would not be a tragedy.
P1: The existence of several other species depends on human intervention. P2: If humans die, they die. P3: So, human extinction would be a tragedy.
P3: The number of species we save is nowhere near the number of species we have killed off. So, in the grand scheme of things, it would not be a tragedy.