I have no idea. Why did God allow the life-long criminal on the cross to convert?
But he converted in public on a cross and became a public living testimony of the truth of Christ, as brief as it was, but the quality of testimony is what matters. So God willed his conversion to be public so others who are lost might see the light and become saved in Christ.
So if Borgolgio perfectly repented of his sins and converted, he would've been a great public living testimony for Catholic truth, even for just a little while before God taking him Home. But that didn't happen. Sure, we humans, many times, can't understand the mysteries of God and His will but it's not unreasonable to think God didn't allow Borgoglio to live longer and more time in public ministry because he never repented and converted.
Absolutely not. The faithful are ALREADY scandalized by Francis. Him converting doesn't change anything. Just like St Paul converting didn't change his past, nor make his crimes against Christianity any better.
Again, it's about saving at least some souls now and in the future. It's not about the past. The past is done. Just as St. Paul's ministry was about converting people to Jesus Christ not about undoing his past crimes against Christians.
The Church does not presume that any person is in hell. Thus, we cannot either.
The Church knows and defines that anyone who dies outside of the Church or dies in mortal sin is in hell.