By the basic meaning of its title, it would seem that an irrevocable trust cannot be revoked. However, in Louisiana, a battle is waging over whether or not that is always true.
Tom Benson is believed to control the largest fortune in the state of Louisiana. In 2009, he signed a succession plan that would leave the fortune in the hands of his daughter and grandchildren after Benson passes away. However, Benson has since become estranged from those relatives. Recently, he announced that he was changing his succession plan to leave everything to his wife of 10 years.
WDSU has more details on this story in "Fight over Louisiana's largest fortune continues."
This case will turn on the exact wording of the original trust documents.
If the daughter and grandchildren are already vested beneficiaries of an irrevocable trust, then it will be extremely difficult to change the trust to exclude them. This is one of the reasons that many people prefer revocable trusts. However, there are tax and other considerations to consider with the different trusts.
While the family with "Florida's largest fortune" hasn't sought my help, the issue of changing or revoking the irrevocable comes up regularly in my practice. Please get in touch if you have questions about revocable vs. irrevocable in your own estate plans.
Reference: WDSU News (January 23, 2015) "Fight over Louisiana's largest fortune continues"