It depends where you killed it from! If you deleted it from the dwnld window, no sweat! Just re-search for the item & re-select it to dwnld again & it will continue where it left off (make sure it's the identical one with the same full size.)
If you deleted from the dwnld window, I don't recommend forcing it to recontinue from the incomplete folder! Sometimes the files forget their dwnld history!
If you deleted it from the incomplete folder in the LW Library window, then there's little you could do except immediately use a deleted file retriever utility.