In his 1786 book, "The History of Heresies and Their Refutation", (saint) Alphonsus Liguiri wrote:
I think the danger of eternal perdition, by dying separated from the Church, should be a sufficient motive to convert every heretic. It was this that made Henry IV [of France] forsake Calvinism, and become a Catholic. He assembled a conference of Catholics and Calvinists, and after listening for a time to their arguments, he asked the Calvinistic doctors if it was possible a person could be saved in the Catholic faith; they answered that it was; "Then," said the King, "if the faith of the Roman Church secures salvation, and the Reformed faith is at least doubtful, I will take the safe side and become a Catholic." (p.634-5)
The logic in the above story is simple: If Catholicism is true, Calvinism leads to perdition; If Calvinism is true, Catholicism might lead to salvation. Ergo, statistically speaking, it is more convenient for salvation to be Catholic.
Naturally, the above is valid if and only if:
1. According to Catholicism, Calvinism leads to perdition:
In my understanding of this, before the Second Vatican Council, the interpretation of the phrase "there is no salvation outside the Church" (Extra Ecclesiam nulla salus) was that non-Catholic Christians could not be saved. This is surely in line with the argument of the story, and what Alphonsus believed. However, after the Second Vatican Council, and without a change in the dogma itself, the interpretation of the phrase allows for non-Catholics (e.g Calvinists) to be saved. In this sense, the argument of Henry IV, from a Catholic perspective, falls apart.
2. According to Calvinism, Catholicism might lead to salvation:
As I read online, the key doctrine about salvation in Calvinism is that of predestination. Besides the seemingly divergent understandings of what this means, at least from what I read, predestination is surely open to Catholics. Or, to say the same, it is not closed to them merely because of being Catholic. In this sense, the "Calvinistic doctors" of the story were right.
Please indicate in the answer if this is not the case (i.e. that according to Calvinism there is no salvation in the Catholic Church).
If point 2 above is correct, then it is just natural to ask: would it be more sensible for Calvinists, from a probabilistic sense, to adopt Catholicism as their faith, just as Henry IV "did?" Or, to put it differently, what is the counterargument in the above story? Why is it sensible from a salvific point of view to remain a Calvinist?
PS: a quick glance at Wikipedia suggests the story of Henry IV might not be true. But that's beside the point.