If his heart is right, no. The evidence of that is if that person continues to grow by the leadings of the Holy Spirit. But can a person believe Jesus is the Son of God and still have a heart "not right before God"? That's the question here.That would be a tragedy I'm sure you would agree.
So the heart seems to take precedence then.
1st John -
"15Whoever confesses that Jesus is the Son of God, God remains in him, and he in God."
According to the same John of the gospel, as long as I confess the above then God will remain in me.
and what is confessing mean? John himself answers in the same chapter-
"2By this you know the Spirit of God: every spirit that confesses that Jesus Christ has come in the flesh is from God; 3and every spirit that does not confess Jesus is not from God."
If I believe both of the above til I die, unlike Simon Magnus, is my heart right?