Once you have it installed, to play Call of Duty: Modern Warfare offline, all you need to do is select the Go Offline option. This will let you boot up the campaign and get cracking with the story, simple as you like.
Yes, in Call of Duty 4: Modern Warfare, it is possible to play multiplayer offline with bots. This feature allows players to practice their skills or enjoy the game without an internet connection.
Shooting Menendez will get Farid killed and he is necessary for the achievement so shoot Harper instead. And finally in the mission Odysseus you dont need to do anything just play through to the part where Menendez takes Admiral Briggs.