All perfect praise be to Allah the Lord of the Worlds. May His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
If the marriage contract was concluded by a Muslim judge then the couple aren`t sinful and the contract is valid although the woman`s guardian (Wali) wasn`t present as he lives in another country. In this case, the judge becomes the guardian of the woman.
In case the marriage was unregistered (Urfi marriage), then it is invalid, and this man woman relation is unlawful. Therefore, they must repent immediately and conclude a valid marriage contract in Sharia court. This sin is the result of following Satan`s footsteps, as reflected in the following verse: "O ye who believe! follow not Satan’s footsteps: if any will follow the footsteps of Satan, he will (but) command what is shameful and wrong: and were it not for the grace and mercy of God on you, not one of you would ever have been pure: but God doth purify whom He pleases: and God is One Who hears and knows (all things)." {An-Nour, 21}. And Allah The Almighty Knows Best.