If your husband truly gave his life to Jesus Christ, then you can be confident that he is now in heaven in spite of all the years he ignored God. Jesus' promise is clear: "Everyone who looks to the Son and believes in him shall have eternal life" (John 6:40).
How could God forgive him and open heaven's door to him after a lifetime of neglecting God? The answer is simply this: Salvation is a gift of God. None of us deserves it, and none of us can claim God owes it to us. Salvation comes to us as a gracious gift from God even to the most undeserving.
Do you remember the two criminals who were crucified with Jesus? One mocked Jesus but the other turned to Him in faith and said, "Jesus, remember me when you come into your kingdom." The Bible says that Jesus replied, "I tell you the truth, today you will be with me in paradise" (Luke 23:42-43). That man had spent a lifetime away from God but when he turned in faith to Jesus, God forgave him and saved him. Thank God for His grace!
At the same time, your husband's life is a warning to anyone who ignores God. What if his death had come unexpectedly and he hadn't had time to repent and trust Christ? The Bible's warning is clear: "Now is the time of God's favor, now is the day of salvation" (2 Corinthians 6:2).