I'm glad that you're in a good place through all this. Change is super hard, especially when it's change in therapy, I think.

I know that even when one person drops out of my group T - or a new one joins - I have trouble with the transition...dealing with loss, with not trusting the newbie, the change in the group dynamic due to the change....ugh.

You are really looking at this in a very healthy way, knowing and accepting that it's going to be hard, acknowledging that you're scared, and knowing ultimately that you will be ok. Good for you!