Taggathias is correct...unfortunately, a person's leaving is frequently unannounced. What bothers me about unannounced disappearances is that the person leaving, perhaps, doesn't realize how much others in their fellowship have come to care about them. Call me overly emotional, but I do get quite fond of people in the fellowships that I have belonged to. I try to maintain periodic contact with those who have left or, in the case when I have left, I try to maintain contact with the individuals that I had grown fond of via periodic emails. When someone leaves abruptly without notice, I invariably send them an email asking them if they are okay and if there is anything I can do for them. If you care about this person, perhaps, sending an email of concern might help bring them back...or, at the very least, put your mind at ease that you have done what you can and may lead to a continuing friendship through emails.