I can't find a definite answer in Church teaching, which doesn't usually engage in speculation of this sort. On the one hand, as you point out, the patriarchs and prophets are considered to have been waiting in the "limbo of the fathers", sometimes also called "the bosom of Abraham"; that is, they are considered to have been waiting "outside" heaven for the fullness of salvation which was given by Christ's death.
On the other hand, we do specifically know that Mary was saved at her conception by virtue of her Son's death-to-be:
Her soul, in the first instant of its creation and in the first instant of the soul's infusion into the body, was, by a special grace and privilege of God, in view of the merits of Jesus Christ, her Son and the Redeemer of the human race, preserved free from all stain of original sin.
(Apostolic Constitution Sollicitudo Omnium Ecclesiarum, Alexander VII; quoted in Ineffabilis Deus. Emphasis added.)
So we know that there was one human being who was saved by Jesus' death before He actually died; but she was a very special person indeed, and it was "a special grace and privilege" that she should have been saved before the death of her Son. Thus, although I don't see any sort of commentary on the subject, I would strongly expect that any other human would have had to wait, as you put it, until the death of Jesus—even those who had been specifically told that they would be saved.