Re-entry required?

[CTKismet]

I've been a US green card holder since Dec 2006.
My current 2 year re-entry permit will expire in October 09.
I will be returning to school in Canada for my last year of study. School will start next week.

And the I will be graduating next year in August. (so approx. 1 year from now)

I do intend come back to US in Dec 09.

Is a re-entry still required???

Any thought is appreciated

thank you