Not an investigation, as Dan Rather fraudulently promised, because Rather and CBS News already know exactly what happened. An "investigation" by CBS is likely to continue the cover-up, providing an excuse for CBS News to gag employees until after Election Day, "due to the investigation." This would have the effect of silencing sources, rather than providing full disclosure.
To put this matter to rest, all Rather and his accomplices really need to do is tell the truth, the whole truth, and nothing but the truth--in a venue not controlled by CBS video editors.
For example, lets start with a live press conference, where Dan Rather answers questions, instead of asking them. It could be televised on PBS or C-Span, if CBS doesn't want to carry it.