I've run across this situation before and was wondering how others handled it. On a firewall, there is going to be a cabinet installed. There are two recepticles that need to be demo'd. The feed is MC and it goes from a box on the joist, into the firewall and then evidently over one web and down into the first rec. j-box. It comes out of the first box and, staying in the wall, goes over to the second recepticle box. It then continues the loop to a third recepticle that is supposed to stay as existing.
As a usual practice, and because I don't want to leave behind wires in the wall, I would disconnect them and forcibly pull the wire completely out of the MC jacket. That is not easy, but so far it has been successful. The more bends in the MC, the harder it becomes and I'm not looking forward to demo'ing the MC to the first, second and third box. I plan on refeeding the third box down the firewall and hopefull there are not any obstacles in the way so I don't have to damage the firewall and repare it.
I have to admit that it has crossed my mind to just disconnect the feed coming down and putting blanks on boxes, to be covered by the cabinet. The old feed into the third box would be capped there and it wouldn't leave a mess of buggered up wire behind if I wasn't successful to remove it.
I'd like to hear others opinions or what they do in such cases. I have a feeling it involves a lot of sheet rock cutting and patching, which is what I'd like to avoid.