1
How does the Rogue Trader Entourage work with attached units?
(self.warhammer40k)
From my reading of the rules, the Entourage as a whole has the Leader ability, while only the Rouge 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 Rouge Trader) are still one Attached unit (until all the Breachers or all the rest of the Entourage are destroyed).