I'm not an expert on biodiversity, although I'd like to be. Of course extinction is forever, and habitat loss is exacerbated by climate feedbacks. But we have to accept change, making less fuss about protecting 'native species' (to me this feels rather like nativism wrt human immigration), and recognise that life on earth has suffered and survived worse calamities in geological history, so it will re-adapt to new situations, if we let plants and animals (including ourselves) move with the climate. We can't save all the old ecosystems (for example from considering thermodynamics of the symbiosis within coral reefs, I have little hope for their survival with combination of higher T and CO2 and SLR), but we might help create new opportunities for new ecosystems in new places. In this context, what matters is the rate of changes - as it takes time for trees to grow, soil to accumulate - rather than 'equilibrium' changes.
I don't know whether the OP was specifically reacting to lack of progress at the Biodiv COP16 in Cali, as well as US election and climate news, but as an old hand at COPs too, I hadn't expected much, at the end of these circuses the only certainty is that the show must always go on (or diplomatic teams would kill their own job). In my opinion both COP processes have got bogged down talking mainly about money, and the UN system as a whole has not been working for many years, so we need some radical rethinking about global cooperation. Nevertheless on a local and regional level plenty of positive things are still happening. Also human population growth is also peaking, or heading that way, on all continents except Africa, and in many countries there is reforestation recently.
In general, bear in mind that many big science consortiums publish reports around this time of year, with extra-worrying headlines, in a bid to influence the COP processes. This is just part of the new-normal seasonal cycle, like the grey skies where I live, but not a reason to lose hope - brighter days will follow.