Once you're initiated, you can't join another NPC sorority. But there's nothing preventing you from joining another group (other than a social sorority) on your new campus - say, a service sorority/fraternity.
As carnation pointed out, you may not get into a sorority if you depledge and rush at your new school - or you may not like the sororities that are there.
It's your choice - but if I were in your shoes, I'd rather be an alum than be potentially left out of the Greek system entirely.
