Never be able to make new ones. We had this very conversation 10 years ago when I had brain surgery. The surgeons warned me that if something were to go wrong, new memories would not stay. My wife and I joked that when I awoke after surgery, I would look at her and ask, who are you. I didn't notice it, but she was scared and crying inside. Then, what was weirder was when I got out of the hospital. We went and watched the movie 50 first dates. My wife cried through the whole movie because that's what could have happened to me.
lose every old one i can remember, too painfull.
lose all my old memories of course, they really aren't that good.
I'd have to say lose my old ones, but dang...there's one or two I'd miss.