Is there a difference between committing the unpardonable sin and just not accepting Jesus and dying in sin?
No. Rejecting Jesus is the only unpardonable sin because it’s the only one that puts a person beyond God’s forgiveness. To reject Jesus is to refuse to allow His death to pay the penalty for one’s sins, and His death is the only remedy for sin God has provided. Therefore a person who rejects Jesus has made it impossible for God to forgive him or her.
Jesus said, “For God so loved the world that he gave his one and only Son, that whoever believes in him shall not perish but have eternal life. For God did not send his Son into the world to condemn the world, but to save the world through him. Whoever believes in him is not condemned, but whoever does not believe stands condemned already because they have not believed in the name of God’s one and only Son” (John 3:16-18).