Game Design Director, David Vonderhaar, has confirmed that “if you prestige and unlock a gun, you pick up right where you left off“. This is all part of the new leveling system in Black Ops 2 MP. Each gun has it’s own level, and you need to gain weapon XP to level the guns up to unlock attachments. So now it appears you can keep your attachments/camos after permanently unlocking the gun you pick.

SOURCE: @DavidVonderhaar