Yes. The object still exists, but if you don’t know the ID and/or Tag URL, I don’t think there is a way to access it again. Nor does it seem like you would need to. You can easily create a duplicate Tag that gets a new ID. I can’t think what the value is in retaining unused Tags.
In the same topic you referenced @Phil_Seeman, the original poster figured out a way to keep using an unused Tag.
I’m guessing the API doesn’t expose these unused Tags, but I don’t know. And again don’t know why you would want them. If they aren’t used in any incomplete or completed Tasks, how much value can they really have?