Disassociation   and disfellowshipping results in the same punishment. If you're disfellowshippped it means that three Elders had a judicial committee meeting and decided to remove you from the organization.
The Watchtower says "disfellowshipping is an action taken by a judicial committee against an unrepentant wrongdoer, disassociation is an action taken by an individual who no longer desires to be one of Jehovah's Witnesses." Shepherd the Flock of God, page 110.
Either way you are no longer one of Jehovah's Witnesses and must be shunned by your family and friends who are JW's. If you're a JW and decide you're not going to practice shunning, you can get disfellowshipped for challenging the Watchtower's Shunning Policy. 
The official rule makes exceptions for associating with disfellowshipped or disassociated relatives and family but this book is only available to Elders. All other JW's are told they must shun their family, even their mother, father, children, etc. ... JW's are told it's 'God's command' not to associate with those who leave the religion.  Therefore even though there is an exception to the shunning rule, JW's don't take advantage of it.
Of course the exception to the shunning rule is not attractive. There is punishment for talking to your relatives who leave the Watchtower but that punishment doesn't always mean you'll be disfellowshipped. Here are the exceptions to the rule from the secret rule book.
"6. If members of the congregation are known to
have undue association with disfellowsbipped
or disassociated relatives who are not in the
l elders should counsel and reason with
those members of the congregation from the Scriptures. Review with them information from the
"God/s LoveN book, pages 207-208; The Watchtower
of ApriJ 15 1 1988, pages 26-30; or the article "Display Christian Loyalty When a Relative Is DisfellowshippedJJ in the August 2002 Our Kingdom Ministry.
If it is clear that a Christian is violating the spirit of
the disfellowshipping decree in this regard and does
not respond to counsel, it may be that he would
not qualify for congregation privileges, which require
one to be exemplary. He would not be dealt with judidally unless there is persistent spiritual association or
he openly criticizes the disfellowshipping decision." Shepherd The Flock of God, page 116 (Secret rule book for Elder's only)
1. The Watchtower says 'disassociation is an action taken by the individual'.
2. In 1981, the Watchtower made it a sin for Jehovah's Witnesses to leave their religion. Here's how they view JW's who decide to change their religion or believe something else. 16 "Persons who make themselves “not of our sort” by deliberately rejecting the faith and beliefs of Jehovah’s Witnesses should appropriately be viewed and treated as are those who have been disfellowshipped for wrongdoing." Watchtower magazine, Sept 15, 1981, p 23, par 16 See Persecution of Jehovah's Witnesses. Freedom of Thought, Conscience, and Religion