First there is the question of ‘what is the law’? A subject I am not comfortable speaking with authority. Some things I know for sure, like worshiping something other than God as god will never be right. First of Ten Commandments, part of the whole Law of Moses, or the ‘Greatest Commandment’ of Jesus ... this LAW is an immutable part of God’s nature. The need to put people to death for wearing cotton-polyester blends seems potentially less of an eternal command.
Moving beyond ‘what is the Law’, let’s briefly touch on what it would mean for part of the law to ‘pass away’. Something GOD declared a requirement, is no longer required by God to meet his standard of holiness. Has God lowered his standards? Did God demand something that was never really necessary? Both are silly positions to even suggest. Thus the LAW is God’s recorded standard for living a perfect life as a people set apart in a true theocracy cannot change until God creates a new (sinless) Heaven and Earth with a glorified people who no longer need any Law in order to do what the God requires. Where God supplies the robes, there is no need for a Law about two fabrics. Where God dwells among His people there is no need for a Law about worshiping other gods.
Yet scripture tells us that we are not under the law. This is true, and this is false. Our relationship with the law is different than that of the Theocracy of Israel instituted by God under Moses and Joshua. There is no salvation to be found for us un the LAW. However much we keep, we cannot keep it all and it will not remove the stain of our sins (those points where we fall short of the Law). This is not a serious problem since the purpose of the Law is to teach us about God’s righteousness and our sinfulness. The Law shows us that we cannot keep it ... which drives us into the arms of GRACE.
There will come a day when we will be perfected and with God. Then there will be no need for any law to teach us what we will already possess in full. Until then, God’s standard of moral perfection can and does not change. On that day, the Law will no longer be needed.