I had the same problem happen to me. Hard drive crashed after a vacation and pictures were lost before I performed a back up. It took a few weeks worth of research and phone calls to get a manager at my local Apple store to approve my request to keep my hard drive for future recovery. Call, or better yet, go to an Apple Store and speak to the highest level manager. Ask them to "please" accommodate your request to keep the old hard drive. They call it a "KBB Keeper" on the paperwork. They handed me my old drive for $0 cost to me. They said they often will accommodate this, but they do not offer it or advertise it.
Have them note it in their computer files for your computer's history so that the shop that did the work can get approval from Apple to release the hard drive to you.
Have a copy of the notation from Apple if you can to be sure the shop that did the work isn't trying to get an extra $199 out of you.
Please post if your logic board replacement worked or not, I may try the same thing.
Good Luck!