Hypotetycally speaking nothing imposes them to write a book and ask publishers to release them after their death.So they don't break the omertà and they will leave to their heirs a lot of money in royalties.
This is actually a very interesting debate between historians. Some historians advocate for the possibility to record the "testimony" or the "story" of people involved in illegal activities and release them only after they died. It's an important part of the history of societies and countries that is often undermined.
It mostly concerns people involved in terrorist activities. The first project of that sort was created by Boston College who interviewed several former members of the IRA and the UVF. In one instance two IRA members admitted to an unsolved murder (Jean McConville) incriminating other people who were still active and not part of the project. British justice tried to seize the tapes and prosecute these guys.
