Are you sure you lost SIM contacts? Could it be that it is only hidden in the phone book but really still there? If so, you can still see the names in conversations which are saved in the history Whatsapp, although I'm not sure. Anyway, Gmail may have saved a copy of your contacts, whether in the initial configuration of mobile activated the option to sync contacts with Gmail automatically. I do not know if any of this will help, but right now I can not think of anything else.