The views are likely to be a pain. Sections, elevations and details with source markers placed in plan view should merge with all settings intact but without any 2D content placed in the views themselves. Independent worksheets and details will have to be recreated from scratch (AFAIK) and their content imported one by one.
You may be able to speed things up a little by publishing modules of all the 2D content and then merging them into the newly created views. The other approach is copy/paste. The publishing bit just allows you to kind of batch process all the copies which saves about half the navigation and nearly all the back and forth.
This will all be a lot easier if your layers allow you to isolate the 2D content.