Extending human empathy to non-human processes is peak anthropocentrism.
The whole notion that the "current trajectory" is somehow objectively bad is ridiculous. It may be bad for humans though.
Maybe I misunderstood because it seems you're claiming if there's no humans around it's impossible to model any phenomena, but we possess abstract thought to make up those situations and define things like degradation in the absence of humans.
While the amount of biodiversity can be measured objectively, the notion of it being "good" is completely made up. You need humans to judge what's "good" and which means that for any "good" kind of future humans are essential and are more important than say biodiversity.
If humanity changes the current environment enough, then it will no longer be the once ideal environment to that continues to sustain humanity indefinitely.
Going on a tangent, a lot of environmentalists have a marketing problem.
Only humans have a chance to save "nature" by bringing life along to the stars. Not sure if we will be able to pull it off, but I see no other option.
Evolutionary adaptation takes a while, so its not nice to change things fast.
So who gets to set the metric?