So, my Courier is supposed to take a new brain for Rex, since his own one is apparently consumed.

Now, there's a curiosity I have about that - something that the quest so far hasn't even mentioned: isn't changing Rex brain the equivalent of killing him? If we take another dog's brain and put it in place of Rex old brain, then supposedly we don't have Rex anymore, but what we should get is another dog inside Rex's body.

If my understandting is correct, then by doing that quest, you fix the cyberdog, but you actually kill Rex. Is this ever mentioned in the game?

Unless everything that is Rex is copied and put on a back up hard drive within his body. New brain put in and everything that is rex gets installed into the new brain along with the other dogs memories.

Mmmmh, it's a guess.... but is this mentioned?

Something about merging memory is mentioned at end game, if you have completed the rex quest.

I believe herne is right. The memories merge. Rex will take on some of the other dogs traits. Three dogs to pick three different personalities.

I see... so I suppose I'm fine if I replace Rex brain? I wanted to be sure that I didn't end up killing the poor guy and substituting him with another dog.

Unfortunately, this process is not fully explained in-game. Dr. Henry or his assistant should have fully explained this. it is left to the end-game slideshow to bring all of your decisions affecting the major factions and NPCs to an anticlimix—an apt term, since the game really doesn't come to a conclusion and the ending is universally disappointing.

I am now going to ask a moderator to move this into the Spoilers Forum before we all get into trouble.

i think the doc puts rex's old memories into the new brain.