Using Session ID to delete abandoned carts

[eluser]Henry Weismann[/eluser]
Hey I have a checkout procedure and want to delete abandoned carts based on the last activity of the session. If I save the session id in a pending orders table will I be able to delete pending orders based on the last activity in the ci_sessions table or if the session id no longer exists?

I wasn't sure if the session id changes for session hijacking reasons that's why I am asking.

PS: I am using the new cart library and its great. I think it could use a way to add line items independent of cart items...like shipping, tax, whatever. Although it might be intended for the programmer to add that piece.