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Well, this is a question about a highly unlikely situation. Some units, such as a vindicare assassin or that space marine scout special character, can choose which model to attack. If the broodlord dies BEFORE his retinue, what happens to the retinue? Does it count as a troops choice, and therefore a scoring unit?
I believe that they do, since they are just a normal squad of Genestealers until the Broodlord gets there as an upgrade unit. Don't quote me on it but I believe that they could capture objectives.
I think they would count as a HQ as the broodlord and his unit count as one slot on the force organisation chart so the genestealers would probably be treated as HQ's as that is what you purchased them as.
They're HQ always. Now, there is a benefit that you get from losing the broodlord, namely that the stealers revert back to being fleet. But they aren't scoring units ever.
~2k of genestealery goodness
~1750points of terminator goodness
Dovie'andi se tovya sagain
more witty remarks to come.