So sorry you are going through this. I have been through a lot of terminations with therapists and all of them were painful.
I am going to be going through another one in October with my therapist of 6 years because I am moving. I am already sad thinking about it. She has been with me through trauma, job losses, getting jobs, losing both parents, losing my cat. I don't know how I am going to deal with it. I have shared more with her than any other therapist.
I wish I had some sage words of advice to give you but I don't. My last therapists I got only three sessions to say goodbye so I kind of understand how hard it is to deal with sudden endings.
Just be gentle on yourself if you can. Allow yourself to grieve. You lost someone important to you. You aren't alone.