Their green card may be considered abandoned, and they might be denied reentry at the port of entry.

They could try applying for a Returning Resident Visa (SB-1) at a U.S. embassy, but approval is difficult.

If denied, they may have to start the immigration process all over again through family or employment sponsorship.

Shorter absences (6–12 months) can also raise questions about maintaining permanent residence, even if technically allowed.