Vivek writes, "My elderly Indian parents received their green cards over 8 years ago but have not been able to live in or visit the United States for over five years now. Recently, they applied for visitor visas and when they received their passports there was a letter asking them to show up at the Mumbai Consulate and surrender their green cards after completing Form I-407. Since it is such a hassle in India to visit the United States embassy or consulates and they are both in poor health, can they simply surrender it at the port of entry on arrival in the US? Can they authorize an attorney to do it for them? Is it possible to mail everything?"
Permanent residence status must be formally surrendered: For anyone who has ever applied for permanent status in the United States, it is as much hassle to get the coveted alien registration card as it is to surrender it. While there are some broad guidelines that if a GC holder stays overseas for more than one year without a reentry permit, he or she has lost the green card or it has become invalid by reason of abandonment, the fact of the matter is that the green card is not formally cancelled until an immigration judge approves it or the alien voluntarily surrenders it. So while technically your parents have abandoned their permanent residence in America, the process is not complete till the paperwork is done because in theory they can try to convince an immigration judge that they have not abandoned their permanent residence status and should be allowed to live yet again in America. By applying for tourist visas and the embassy issuing them, it is merely a formality that needs to be completed for a smooth process for them as well as the United States Customs and Immigration Departments.
Now, regarding surrendering it by mail, apparently this option is not available to Indians (nationals of other countries should check with the local embassy because in many countries, the paperwork can simply be mailed -- on the embassy website search for the keyword I-407). She will have to bring it herself at one of the consulates in India. For similar reasons, Indian citizens are not able to use the services of an authorized agent or lawyer to renounce the green card.
What happens at the airport on arrival? Except for citizens, entry into the United States is not a right but a privilege. The decision is made at that point of time by an agent at the border or airport and is final. There is no appeal process or request to speak to a higher level officer. So if you show up at the airport (even with a valid visitor visa) without actually formally surrendering your green card, the agent will still deal with you as if you are a permanent resident arriving after abandoning your status. Be prepared to be grilled (maybe even in a secondary questioning area) about all sorts of issues including unpaid taxes. It is also likely that not only can the officer confiscate your green card, revoke your permanent resident status, and put you on a flight back home (never forget that a visitor visa provides no guarantees to entry). Alternatively, your green card maybe cancelled, but you are allowed entry in order to appear before an immigration judge. For someone who plans to surrender the card anyway, this is huge hassle because the court date could be months away and without appearing before a judge, you cannot leave the United States (which would amount to self-deportation and can have severe consequences like bans on reentry). So the right way to do this is to actually surrender it formally at the consulate in your native country and then keep a copy of your stamped Form I-407 with you while traveling to the US every single time (while the US databases will be updated to reflect that you are no longer a permanent resident, at the time of airline checkin, the agents will not let you board the plane unless you show the stamped Form I-407 to prove that you are no longer a permanent resident but will be using a tourist visa to enter USA).