No. Just because it's not being used doesn't make it OK to take it. That said, I would do whatever I could to talk the person into making use of the miles. Perhaps they can gift it to me, or the person can donate it to a non-profit. If I had a car that wasn't running, and I wasn't planning on getting it fixed, but I kept it in my garage, I will be extremely upset if someone came and stole my car. Yes, even if I wasn't planning on getting it fixed. My response if that happens, would be, "Why didn't you just ASK me? I would have given it to you for free, or bartered for something. Instead, you took something that wasn't yours to take."