Rambles from a fully integrated plural system
If your therapist ever insists that the only way to be healthy is to fully fuse (as in, integrate all of your system), you have every right to turn and run in the opposite direction. Not only is it just flat out wrong, but I'd argue that it's malpractice!
The ISSTD's 2011 Adult Treatment Guidelines for DID state that "clinicians should not attempt to press for fusion" (pg. 144). Clinicians with plural patients must know that "a considerable number of DID patients will not be able to achieve final fusion and/or will not see fusion as desirable" and that "a more realistic long-term outcome for some patients may be a cooperative arrangement" where they are able to harmoniously live and work together as a system. (pg. 133-134).
There aren't guidelines when it comes to non-DID plurals but if fusion isn't required for the plurality in DID, it certainly shouldn't be required for other manifestations of plurality.
If your therapist is pressing for the extreme opposite of all of this, though, (i.e. telling you that fusion is impossible or forcing you to form new headmates), you should also turn and run in the opposite direction. How you recover and live with your plurality is entirely your decision. A good therapist will help you explore what's healthy for your whole system and support your pursuits.
I see it often in the plural community — this fear of therapists forcing fusion onto us. How likely is it to actually happen, though? I wonder about that a lot. Sure, there are absolutely people who believe that final fusion is the only right outcome for plurality, but they're certainly not in the majority.
They were the majority in the past, but I don't think they are in the present. Not after decades of plural advocacy and challenging the Western idea that multiple selves are unnatural. The idea that one simply cannot be healthy as plural has been contested from the very beginning.
I'd argue that Richard Kluft is one of the spearheads of final fusion in DID treatment but even he has acknowledged that it's not the only option. In his 1988 paper on treating multiples post-final fusion, he stated (likely through gritted teeth) that "several therapists have expressed and explored the view that a negotiated settlement or reconciliation of the personalities, considered a stage in treatment by most, may be a more readily achievable and/or preferable end point or goal than unification" (pg. 213).
In 1983, a New York Times magazine "Inside The Divided Mind" showed a psychiatrist advocating for both fusion and healthy multiplicity. "It seems to me that after treatment you want to end up with a functional unit, be it a corporation, a partnership or a one-owner business," said Dr. David Caul (last paragraph). In the third issue of Many Voices, a social worker stated that "not all multiples 'integrate' and become whole. That is their choice, and that choice is okay. . ." (pg. 7). That's from 1989!
Perhaps one of the most profound examples, to me, is Kymbra Clayton's 2005 paper "Critiquing the Requirement of Oneness over Multiplicity." If you can stand the medical jargon, I really recommend reading it. Clayton paints a clear picture of how the past treatment of DID has been colored by (primarily Western) biases. I think that we can see the beginnings of those biases being unpacked in the 2011 treatment guidelines I quoted before. If you compare them to the outdated treatment guidelines from 1997, the changing views are very apparent. Acceptance of plurality has been growing, and it will continue to grow!
Maybe hearing these things is not enough to put you at ease, though. So, let's talk about my own experience.
I am a full fusion! I was diagnosed with DID but I no longer fit the diagnosis; it remissed well before our system integrated. We are still plural despite being fully integrated. No part of us was erased.
Our therapist never suggested final fusion to us. They came from a culture where multiple selves are the norm, not the problem. We were never made to feel weird or particularly special for being plural, which was really beneficial to our healing. Western ideas of a singular self are unusual and I can't help but agree.
We did not actively pursue final fusion, either. We never sat down and decided which parts should combine. It happened to us naturally over the course of our recovery. The lines between us gradually began to fade away and we experienced a peaceful blending. You must understand that we could've reversed it if we wanted to, but we didn't because it felt so amazing! We just let it happen and eventually all of us fused.
None of this was forced onto us by our therapist. We were only ever supported in our choices and the way we forged forward in our own recovery. The decision was ultimately ours to make, just as it is for you.
Please always remember that you are the one in control of your recovery. You get the say in whether you fuse or not. Maybe it's right for you, maybe it's not! No one else gets to determine the answer except for you and your system. If a therapist ever tries to pressure you one way or the other, they aren't a good therapist and they aren't worth your time!