As a general rule, a valid permananet residency card allows you to depart the U.S. for up to one year. If you are planning to depart the U.S. for more than one year, you should file an application for a Re-entry Permit (see www.uscis.gov for information). If you intend to eventually file for naturalization, the trip should generally be limited to under six months. Regardless of the length of trip, it is important to be sure that you properly maintain your permanent residency status while outside of the U.S. (i.e., by continuing to file taxes as a U.S. resident, etc.). More information on proper maintenance of your permanent residency status can be found at www.uscis.gov and www.goellaw.com.
a reasonable period of time. each case like this depends on a variety of factors. go get a consultation from J. David Maxey
BIA Accredited Representative
Refugee and Immigrant Services
Commonwealth Catholic Charities
540-342-7561 ext. 304
he should be able to help. there is a form that you can file in advance of your leaving to preserve your right to return.