For Huygens Nodelocked and Floating licenses the end of your maintenance contract with Scientific Volume Imaging can be seen in the License String of your Huygens Software, after the label "eom".
Start Huygens and go to Help > License overview. Your License Strings will be listed; they will look like this one:
eom2017Aug01is the end of maintenance date of the license.
More details on what this contract includes can be found here.