Once you have deleted your Snapchat account, can the people who were your friends still see the account?
No, they shouldn't. Once you delete your account, it should disappear from all your friends lists and it shouldn't be available anymore. If your friends can still see you on their lists, better visit the official support website and try to connect to your account. It's possible that the deletion process had failed. The only thing that you can do in this case is to try again to remove it.