Hmm... from my research I have to disagree with that. You can always search for it yourself about integration and fusion to just be sure of what I am about to say but here it goes... when Alters are ready to fuse (and I do mean fusion and not integration, these are two different things) that amnesia is somewhat "fixed" because as the word itself explicits - it is the process or result of joining two or more things together to form a single entity - fusion! Now sometimes fusion is ideal and when it happens it ends up being a good thing because those alters ended up conecting well and all those memories and personalities blended with each other properly... other times... not really! Not at all! So, to become "one" is sometimes not ideal for a system! Some systems do not wich to fully fuse or even integrate! and this is a long ass comment already! DID is something very interesting to read and learn about but also a very harsh disability!
I completely agree with it being interesting to learn about and being a harsh disability. Im still relatively new to my exploration of what it is, as i am guilty of believing what media portrays it as, like in the movie Split. It wasnt until a couple months ago when i found a youtuber with DID called disociadid who works to raise awarness on what it actually is that i started trying to learn about it, so i appreciate the information :)

Actually wouldn't it work better if all of them just become one again? Because each of them is some few memories. He could be one normal person with all of his memories in one personality again. Need to accept his whole life as one