If the Rogue Trader Entourage is attached to a squad of Imperial Navy Breachers, and someone uses Precision to kill the Rogue Trader; now that there is not a character in the unit does it split into 2 units on of breachers and one made of the rest of the Entourage?
From my reading of the rules, the Entourage as a whole has the Leader ability, while only the Rogue Trader itself has the CHARACTER keyword. The Leader is used to combine Leaders and the bodyguard unit into one Attached unit. The CHARACTER keyword actually come into this, only for the Precision keyword as you described.
So in your example the Breachers and the Entourage (now sans Rogue Trader) are still one Attached unit (until all the Breachers or all the rest of the Entourage are destroyed).