theres a scene in EP1 where you come across a recording of breen talking with one of the advisors about getting put into a host body right before the final battle of HL2
Then suddenly an advisor pops up on screen and triggers the alarm and one of the advisors in an escape pod shows up below you alluding that, that very slug is breen in his host body and you only saw his human body die.
If thats the case than there was no way his human body could talk without its brain and it was breen taunting you from his slug body not his human one the one that perished.
and also the concept art that was released for EP3 shows advisors flying around the Borealis, so he might actually have had a part in EP3
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