I completely understand. Rationally you know that it's not an abandonment. She retires, she won't have clients anymore, so she can't be your T. But your feelings stays exactly the same. Whether she'd abandon you or whether she retires: She won't be there for you. That is your side of the reality. And that stirs up a lot of feelings of sadness and anxiety. And the feelings are equally real and true.

Only in this case your mind might blame you, because 'you are wrong, you know she didn't abandon you and yet you still feel bad'. I don't believe in that kind of logic. You feel what you feel. And if you feel it, it is true. No matter what.
So I hope you're kind to yourself. You deserve it. This would scare most people in therapy, I bet. I would completely freak out.

And the unknown is scary. Absolutely. But you'll be fine. Hang on.