Green Card holders tend to lose their lawful resident status in America, if they remain abroad for an extended period of time. If you lose your immigration status, your Green Card will be revoked and to get a Green Card again, you need to start the Green Card process all over again. In order to avoid such circumstances, you need to be careful while you plan to travel outside the country, after you become a permanent resident.
Green Card holders may travel abroad for less than a year with their permanent resident cards but if the US immigration officers find that you have plans to settle in a foreign country and abandon your status in America, they may not allow you to get into the United States. In such cases, you need to make all attempts to prove that you will not abandon your lawful status in the United States and that you do not have plans to remain permanently in a foreign country. You may be granted entry into the country only if you convince the immigration officers and prove that your travel was only temporary.
Your US Green Card will be revoked if you remain in a foreign country permanently as US Green Cards are given only to the foreign nationals who look forward to make America their permanent home. In some cases, you can prove that your travel was only temporary if you are still employed in the United States and if your home is in the United States. You may be permitted to re-enter the country if you had to remain in a foreign country for a certain period of time, to complete a short term course. Similarly, your family in the United States and your businesses in America, will also help you to prove that you do not have an intention to live in a foreign country on a permanent basis.
If you had to remain with your sick family member in a foreign country, while returning to the United States, you will have to bring with you, the hospital records or a letter from the doctor who treated your family member. However, all this will help only if you had remained abroad for less than a year and you may get into trouble if you had remained in a foreign country for more than 356 days. You may lose your Green Card if you remain abroad for one year or more. That can be avoided, if you obtain a re-entry permit before you leave America and that permit will help you to get into the country. But you may not be able to apply for a re-entry permit while abroad and you need to apply for and obtain this document while in America.