I agree with those of you who say you're a member for life of any GLO, but it's how much you'll be able to participate after college that varies.
For instance, Sigma Alpha Iota currently has around 120 alumnae chapters. And our alumnae chapters are just as active as the college chapters, which is wonderful, because I like knowing I'll be able to be an active SAI for the rest of my life.
However, I know that Tau Beta Sigma does not have alumni chapters or anything. I was talking to one of the sisters here who says you can pay for life membership, but there's not really much opportunity for participation after graduation.