My understanding is that more current thinking around DID treatment does NOT push for integration, but rather, cooperation, communication, and collaboration among the parts/alters, so that your system function better as....well...a system. While integration CAN happen, it's not something you can or should force, as it can end up being more like (being experienced as) a "deletion" of a part/alter than an integration. Sometimes parts can and will age progress, and sometimes not, but this is something that just happens in the course of treatment, not something you can make happen. This approach to DID takes into account that parts exist for a reason and that they have a right to exist if that's what they/you want. Many times, people with DID and/or their parts have no interest in integrating and therapists who push for it are not respecting client autonomy.

Just adding another perspective to the conversation...