The Bible doesn't tell us how most of the original 12 disciples died although there is no evidence to suggest any were taken directly into Heaven. Only two persons (other than Jesus) were given that honor: Enoch (Genesis 5:24) and Elijah (2 Kings 2:11).
Of the original 12, only Judas died a shameful death, taking his own life after betraying Jesus for money (see Matthew 27:3-5). Both the Bible and early church records indicate all the rest died because of their faith in Christ a faith they refused to deny. Our last glimpse in the Bible of one of the Twelve is of John, in prison on the island of Patmos "because of the word of God and the testimony of Jesus" (Revelation 1:9).
Why were they willing to suffer and die for their faith? The reason was because they were convinced the Gospel was true. They had known Jesus in the flesh, and they also had seen Him suffer and die. But more than that, they had witnessed His resurrection and ascension into heaven. They could say with Paul, "I know whom I have believed, and am convinced that he is able to guard what I have entrusted to him" (2 Timothy 1:12).
You and I today know of Christ because of their faithfulness, and their commitment to bring the Gospel to the world. Is your faith in Christ, and are you seeking to share the good news of His salvation with others?