Why are you getting rid of it? And how? Once you register the key no-one else can use it anyhow. It is still a good game.
I could never play the multiplayer mode because of an issue that I discovered on their forums was common to many who bought it and had the same problem. Their tech support response was atrocious, to say the least. I would log into a server and it would log me out after about 4 minutes of play and said my EA connection was lost. Their forums said it was an "issue" with my router, so I went through the steps setting up the ports on my router according to their instructions (more than once, methodically) and nothing worked. I tried resetting my router and even flashed the router with the firmware update available and again nothing worked. I never had this issue with any other game I've played, with the same router I have been using up until now, so through deductive reasoning, the problem was with the game. So, I decided to get rid of it, since I had already played the single player game already, and Dave said there were no plans to have a BFBC2 server at any miniLAN's, so it is essentially useless to me now.
My understanding regarding the registration is that if you close/deactivate your EA account that is tied/associated to the validation key, you should be fine.