The aim of DID therapy is NOT to "make everyone disappear". The first step is to develop a happy and balanced life as a system. The second step is to heal the traumas. The third step is to learn how to live without the traumas. Fusion is no longer a requirement. Forced fusion never lasts anyway. It's best to let fusion happens spontaneousely, when the system as a whole feels that it's the right time to do so. Some will never fuse and it's okay. (I did not intend to fuse and well... I kinda woke up like this one morning...

Moreover, nobody "disappears" in a fusion. It is more of a feeling of "I am X and Y at the same time, their feelings are mine too, their thoughts are mine too". A good DID and trauma therapist will never try to make anyone disappear. If you meet someone who says they want to make someone disappear... RUN.
Do not hesitate to have a look around the forum, read the journey threads, have a look at the ISSTD Guidelines, or at books like "Coping with trauma-related dissociations" and "Healing the fragmented selves of trauma survivors" to better understand what modern DID therapy is all about. This way you can see if it is the right choice for you, with the full informations.
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Morwan.