You're a permanent resident until you formally renounce permanent residency at a US embassy or consulate. Some may permit mailing in your green card, others require you to appear in person. However, the process is or was free when I went through it.
I think there are other ways of losing permanent residence, but the only guaranteed ways are when you renounce or when the US takes it from you. Either way, you better have written proof.
If you're a long-term permanent resident (8 years or more), then you're subject to the same expatriation tax rules as US citizens. The IRS agents that I spoke to were all friendly and helpful, but unfortunately none of them knew the expatriation rules. It wasn't as bad as it may sound, but it wasn't fun either.
You also have to file a preliminary tax return before you actually leave the country (informally called the sailing permit).
Anyway, just leaving the US isn't good enough when you're a permanent resident and until you're through the process you're on the hook. And don't forget to meet FACTA requirements for the year in which you gave up PR...
What sanctions are available to the USA in case of non-compliance if you do not ever return to the USA?
Personally I find all this 'citizen as property of the state' stuff to be rather revolting, and in direct contradiction of such sentence fragments as 'the land of the free'.
I don't know. My impression is that you don't officially lose your status until some US government official or agency confirms it. Presumably, you may not have intended to give up PR. Maybe you had a stroke or you were unable to meet the requirements through no fault of your own. But I'm speculating. I don't know.
As for the IRS, the rules are in the instructions to form 8854[1]:
> Date of termination of long-term residency.
> If you were a U.S. long-term resident (LTR), you terminated your lawful permanent residency on the earliest of the following dates.
> 1. The date you voluntarily abandoned your lawful permanent resident status by filing Department of Homeland Security Form I-407 with a U.S. consular or immigration officer.
> 2. The date you became subject to a final administrative order for your removal from the United States under the Immigration and Nationality Act and you actually left the United States as a result of that order.
> 3. If you were a dual resident of the United States and a country with which the United States has an income tax treaty, the date you commenced to be treated as a resident of that country and you determined that, for purposes of the treaty, you are a resident of the treaty country and gave notice to the Secretary of such treatment. See Regulations section 301.7701(b)-7 for information on other filing requirements if you are such an individual.
EDIT: These are the rules for long-term permanent residents (8 years or more). I don't know what the rules are for other permanent residents, if there even are any. But you're probably better off if you clearly state your intent and file I-407.
Can you use the systems rules to work around the system?
My guess would be "no". The rules are interpreted by the system to benefit the system. If this means that the rules are arbitrary, capricious, and inconsistent... so be it.
I think there are other ways of losing permanent residence, but the only guaranteed ways are when you renounce or when the US takes it from you. Either way, you better have written proof.
If you're a long-term permanent resident (8 years or more), then you're subject to the same expatriation tax rules as US citizens. The IRS agents that I spoke to were all friendly and helpful, but unfortunately none of them knew the expatriation rules. It wasn't as bad as it may sound, but it wasn't fun either.
You also have to file a preliminary tax return before you actually leave the country (informally called the sailing permit).
Anyway, just leaving the US isn't good enough when you're a permanent resident and until you're through the process you're on the hook. And don't forget to meet FACTA requirements for the year in which you gave up PR...