When I disconnect sections I routinely follow some basic steps to assure that I don't loose 2d information. First I move all of the lines, fill etc. to another layer, then cut everything to the clipboard, and paste it back to the same location. Archicad has the ability to rebuild (display - section/elevations - rebuild) sections after they are unlinked. Unfortunately when this is done anything drawn on the original layers is replaced with what is generated from the model, although the section is still unlinked. This is useful for updating changes that have occurred since unlinking the model, but only if you have taken the above mentioned steps to protect your 2d data.
