Keep in mind that, if you leave for more than 6 months, unless you qualify for an N-407, you will lose all the time you have built-up to become a US citizen.
If you don't care about becoming a US citizen, and if you're not abandoning your US residence, you can file for a Re-entry permit.
Meet with a lawyer to make sure your departure won't have horrible long-range impact on your future in the US.
PROFESSOR OF IMMIGRATION LAW for over 10 years -- This blog posting is offered for informational purposes only. It does not constitute an attorney-client relationship. Also, keep in mind that this is an INTERNET BLOG. You should not rely on anything you read here to make decisions which impact on your life. Meet with an attorney, via Skype, or in person, to obtain competent personal and professional guidance.