Travel soon after greencard interview

[vchamala]

My parents have greencard interview this Friday (10-22-2010). They need to travel to India 4 days (10-27-2010) after the interview. Assuming they are approved, can they travel without having the physical greencards with them? Based on some online posts, there is a very slim chance the officer will stamp the passports. If they don't get stamped, can they travel out? I can mail the cards to India later.

I appreciate a response in this urgent matter as I'm pressed on time.

[immihelp]

They need either the physical card or the stamp in the passport.