Do you not believe that there are many Catholics who are saved? Though under a legal system, the individual can still believe. And is not faith all that is required?
You can't be saved mixing law, any kind of law, law of Moses or law made by man, with grace.
The grace of God is a free gift and comes only from God. If you add to that, and I mean anything, that grace is made of none effect.
The Catholics who come this knowledge are saved immediately, but they must separate themselves from that law, whatever that law may be that voids grace.
That's what's happening with many former Catholics, they are coming to the knowledge of the truth and getting out.