It is necessary when the sin involved has been precisely the sin of lying about what the Church teaches.
The entire cadre of pro-abortion “Catholics” have been teaching the whole Church in America that a person can be pro-abortion and in union with the Church.
That is the sin that requires public retraction.
Since there are priests and bishops in strategic posts who participate in teaching that heresy, this is not going to happen. Kennedy will be permitted to die without repenting, because the only kind of priest who will be allowed near him will be a priest who is “safe,” or “tame.” I.e., a Kennedy-family toady. Kennedy will have a big, splashy funeral, and the scandal will continue.
When he dies, Kennedy will have to face God and accept his judgement. Frankly, whether or not his coffin gets splashed with Holy Water and the priest creates a cloud of incense around it is irrelevant, at that point. I've never let the CINOs, or the priests who allow them to continue in their error, determine what I believe, or how I practice my faith.