May I ask who has disappeared from your life? I know a saying someone told me once when I complained that many of my friends were gone, "The people that are in our lives now are there because they should be there, they want to be. And the people who aren't there are the past, they are gone because they have left." I miss past friends, people meaningful to me, but I try to be optimistic for the future! So.. don't worry. ^_^

you should keep on touch..

It is hard to say as you haven't given any other details. Has this person died or is actually missing and can't be found? Or are you referring to a boyfriend? It is up to you to decide what to do. If it's your boyfriend, then after a period of missing that person, you might feel happier and be ready to make new friends.

depent who is the person, but generally you must traverse this ordeal by yourself, like it or dislike it you have no choice you need to be strong.