In all seriousness... I have to ask, was this disappearance in an online situation? It's all too common with both men and women.
The number one reason I've found for this behavior is that they like attention from a lot of people. They disappear because they're married, already in a relationship, and/or wooing someone else.
They come back to you when they aren't getting enough attention from their other interests or after they've been dumped by someone else. I've seen this cycle happen time and time again, even from the most popular and "Godly"-sounding people on some of the sites I've been on. They keep using their popularity to deceive others and break their hearts, and I have no idea why it doesn't seem to bother them at all.
I've been in several situations in which guys like to see me as The Fallout Girl. We start talking. They like someone else and tell me all about her. They ride off into the sunset with said girl. The sun eventually sets and the storms come crashing in. Then they suddenly reappear because they want a female shoulder to cry on and also see me as "The Spare" (a female they might be able to start something with if their number one pick doesn't work out). I've finally gotten smart and cut anyone like this out of my life.
I'm a lot happier, and you will be too if you cut people like this out of your life.
Now of course sometimes people do have a legitimate reason, such as a family illness.
But the number one reason I've seen this happen is because you are not the only one they're trying to talk to.