A picture would help, but if it is definately not being used I'd think you could do the work.
From what you described, I invision the top half of the pipe showing and the bottom half is imbedded in concrete. If this is correct, I would assume you could break it apart with a sledge hammer, then fill the void in with some sort of cement mixture.
From what I have been told Hydraulic Cement is what you would want to use anywhere it terminates the house/wall.
In the past when I removed sections of cast iron, I've used a sawsall with a good metal cutting blade, but be prepared to go through a few blades. Recently I had to cut a line out and ended up putting a metal cutting blade in my circular saw and that worked great!! Can't go all the way through, but it's a good start and the sawsall finishes.
If there are any lines going vertical, make sure they are supported very well before removing any horizontal lines!!
Hope that helps!