"we realize that some species have disappeared, and in their wake, others are going too, and we are left with a homogeneous ecosystem "

Species come and go all the time. Globalisation just made it a lot faster. So there will be imbalances and local system collapsing and temporary a dominating species etc., but alltogether the diversity of species will be increased, with fast global exchange. Because there are more candidates to fill a niche.

Local established ones still have a home bonus. Their DNA is adopted to the local climate and soil, unlike the invaders. They won't vanish anytime soon.

The thing really threatening diversity are monoculture fields with pesticides.