So what you are saying is Koalas exist better with the trees and without the koalas a single Eucalyptus exists just fine.
Imo G-d made the trees and koalas together. And means them to be together.
I'm less sure G-d intended us to separate the Koala from their... his. Trees.
Now as for Aussenseiter. There's room for concrete and discreet perceptions of the ship of Theseus. However. They aren't "the ship" still. Subtract the rest of the universe and theseus and his ship cease to be problematic.
As far as the sailors are concerned the ships are real and beneath them. However at some point the world can no longer continue to provide planks and rope and sails. Or the world itself breaks apart. Consuming its ships of theseus.
So perhaps the simplest answer. Is yes. It's the same ship so long as you are able to go on believing it is so. And that is fine. It's also a delusion to ascribe a moral or ethical judgment upon such a belief.
Don't worry. I love koalas. On their trees. Not my person. Unless it's a really cute Koala print dress!