The limits to salvation, whatever they may be, are known only to God. Three truths above all are certain. God is a holy God who is not to be trifled with. No one will be saved except by grace alone. And no judge could possibly be more gracious than our Lord and savior, Jesus Christ.
Religion is a complex matter.
Nevertheless, by grace, despite all disobedience, Christianity offers the truth of the gospel. Although other religions may enshrine various truths, no other can or does affirm the name of Jesus Christ as the hope of the world. God has made salvation available to all human beings through Jesus Christ, crucified and risen. How God will deal with those who do not know or follow Christ, but who follow another tradition, we cannot finally say. We can say, however, that God is gracious and merciful, and that God will not deal with people in any other way than we see in Jesus Christ, who came as the savior of the world.