Let's clarify the definition of "sin". Sin is often defined as performing acts that are contrary to specifically noted prohibitions in scripture. In the Old Testament, prohibitions against eating unclean animals, specific instructions about performing certain rituals and ceremonies, etc.
I believe the Biblical definition of "sin" is not so much about actions (dos and don'ts), but about our relationship with God. Sin is really unbelief, and as James taught us, our faith or our unbelief in God is manifested by the things we do (see James 2).
In John 16 Jesus speaks of how the Comforter, when He comes, would reprove of sin not because of a failure to keep ordinances (which the Pharisees excelled at), but because of unbelief.
And when he is come, he will reprove the world of sin, and of righteousness, and of judgment:
Of sin, because they believe not on me;
The Pharisees and religious men of Jesus' day lived spotless lives according to the law, but they were the greatest sinners of all, because they simply didn't believe His message. Outwardly they appeared holy and righteous, but inwardly they were "full of dead men's bones".
Matthew 23:27 -
Woe unto you, scribes and Pharisees, hypocrites! for ye are like unto whited sepulchres, which indeed appear beautiful outward, but are within full of dead men's bones, and of all uncleanness.
Performing various actions is often considered "sin", but true sin is failing to take God at His Word, which becomes manifested by our actions. To answer your question pointedly, failing to take God at His Word will always be "sin".