First of all, the WT tell this lie to the rank and file:
Two factors—which must coincide—result in the disfellowshipping of one of Jehovah’s Witnesses. First, a baptized Witness commits a serious sin. Second, he does not repent of his sin. http://wol.jw.org/en/wol/d/r1/lp-e/2015287#h=5
Now, of course WE know that's not true. My wife for example when she was DF'd a few years ago was genuinely repentant. She confessed immediately after doing what she did. She was distraught, downtrodden and ashamed. She was DF anyway. But of course the rank and file think a person is disfellowshipped because they obviously wernt repentant for what they did.
Disfellowshipping may bring the wrongdoer to his senses. Jesus once spoke of a young man who left his father’s home and squandered his inheritance on a life of debauchery. The prodigal son learned the hard way that life outside his father’s home was empty and heartless. The son finally came to his senses, repented, and took the initiative to return to his family. (Luke 15:11-24) Jesus’ description of the loving father who rejoiced at his son’s change of heart helps us understand Jehovah’s feelings. “I take no pleasure in the death of the wicked, but rather that someone wicked changes his way and keeps living,” he assures us.—Ezek. 33:11. http://wol.jw.org/en/wol/d/r1/lp-e/2015287#h=19
Tell me. When the prodigal son returned. How long did he have to wait before his father embraced him back? A year? Two years? No, he welcomed him back immediately. Those who stop their sinful course and repent should be welcomed back right away.
I understand the need to keep the congregation clean. Remember, Paul said "let him be like a man of the nations". Tell me, how to witnesses treat their non witness relatives or neighbors? Sure, they dont have much to do with them, but do they shun them??? No. They just have limited contact. THATS how a DF person should be treated.
They shouldn't be emotionally blackmailed to come back so they can get their parents back, or the children back, or their siblings back.
1 Corinthians 5:11 - But now I am writing you to stop keeping company*+ with anyone called a brother who is sexually immoral* or a greedy person+ or an idolater or a reviler* or a drunkard+ or an extortioner,+ not even eating with such a man.
The key phrase here is "anyone called a brother". If someone leaves, they're not calling themselves a brother. And if someone was "an idolater or a reviler* or a drunkard+ or an extortioner" then surely we wouldnt NEED to be told not to hang around with them. We wouldn't want to anyway.
There are other reproofs that would be beneficial for someone who has strayed but genuinely wants to serve God. Shunning them is so the opposite of Christianity its unreal.