Does the numbness always go away after chin implant ? I'm still number after 12 days.

At 12 days after placement of a chin implant, there still would be some expected swelling present.  It would not be out of the ordinary to have some temporary numbness of the lower lip and in most cases, this should resolve completely over time.  It could take several months however.  Normally, if the implant is removed, there should be no deformity afterwards.  

Chin and lower lip numbness is a risk of chin implant surgery, since the mental nerve exits the mandible just off to the side of where the chin implant sits.  A little stretch from placing the implant can result in temporary chin and lower lip numbess.  However, rarely, the nerve can be injured as the implant is placed.  Its tough at this point to see which has occurred.  I would give it some more time, and hopefully the numbness should resolve.  Removing the implant can be done at any time, and should result in the appearance that you had prior to surgery, not really any different.  Good Luck!