I think that biologically speaking we will always be transgender/transsexual/whatever. Even when it is hard to see or remember the fact that we have come from A to B doesn't actually go away. I had a dog when I was little that would refuse to look at you when he did something wrong. He would hide his head in the sofa, turn away and would even keep his eyes tightly shut when you tried to force him to look at you. I understand the desire to disassociate with what came before but it is still there. Shut your eyes as tightly as you want, what was once a throw pillow is still nothing but fluffy white innards all over the living room floor. File it away and move on, own it or it will own you.
Transition itself ends, it's even part of the definition. Maybe we all have to figure out when it is over for us. For me it was physical but more importantly social transition. I haven't had my surgery yet but have considered my transition over years ago when my social transition was done. I have integrated and live the only life I have ever wanted. I have a friend that started to transition when I did, she is on the waiting list to have her surgery and that is her ultimate goal of transition and when she says her transition will be over. Social transition was never a priority for her, she loves being in between, loves being a question mark. From the beginning she said that she would be a tomboy, it fits her perfectly and oddly enough, she gets misgendered more when she dresses more feminine.
Life seems to get put on hold when we start to transition, maybe we never actually unpause it but we are living again and our gender is for us what it has always been for the rest of the world, a nonissue. I would guess that is the point when our own transition is over. No diploma, holy cow moments long gone, we don't even remember when the weight we carried disappeared and life just moved on. We will have scars of being born a different gender the rest of our lives, sometimes they may even be painful, but the healing will be done.
What are we when transition is over? I am not going to try unraveling that, I just don't know what definition fits. I feel feminine inside and out and the world treats me like a woman, that really works for me and I am content.