May I ask you how long did it take from arrival in DUS to catch the last ICE train to NL? I am afraid the time is not enough to meet the last ICE.
If you arrive in DUS airport on time and get out of the immingration and customs check quickly. It is quite OK for you to catch the last ICE. I even had a meal in DUS.
After you arrive in DUS airport, just take S7 to the DUS Hbf. It takes only less than 15 mins. Don't worry.