Not sure if this includes other services like Gmail Labs, but I relied on "attachment reminder" throughout college. It has saved me multiple times, including now in my professional career.
No, Gmail Labs is separate and is not being shut down.
I may be wrong, but I think it's been rolled into the main product. A few times, recently, I've been prompted as to whether I've forgotten an attachment, and I don't recall ever turning that Labs feature on.