When doctors first started treating DID (then MPD), they thought that the only way to become "better" was if everyone in the system merged (or integrated) into one person. They finally understood that some systems could not do that, and still other systems would completely integrate only to split back appart because it was too much too soon. What most people strive for now is cooperation between everyone within a system rather than focusing on integration as an end game.
Our system is not fully integrated, and I doubt that we ever will be: there really is no need. After many years of hard work, we do fully cooperate and trust each other and we are able to talk to, and interact with, one another. We pick up the slack for each other and help each other out when we can. Multiplicity is really the only thing we know, I can't imagine living life any other way. (In fact, I really can't understand how singular people manage to do as well as some of them do.)
Once upon a time, we did very much suffer from DID. Things were very chaotic and there was a tremendous ammount of in-fighting, mistrust and deception. We lost time and couldn't keep track of our schedule, finances or realationships. We could barely even communicate with each other.
We were able to turn things into a postive by first learning how to communicate internally so that we could build some trust amongst ourselves. After that, it was important to learn the way our system worked, what we were capable of, how our particular pysiology worked, what our strengths and weakness were and how best to compliment one another.
It's a long and difficult path, but many people have taken that journey and it's completely doable...not to mention incredibly rewarding. It has its ups and downs, but that just life on life's terms. And no matter what, you're going to have to live this life anyway, so you may as well live it trying to improve your lot.