If this were me then I would follow the action plan below:
Assuming you have their email, inform users via email that the feature will temporarily be going away
- Make sure to include a start date at minimum and an end date if possible
Wherever this feature is, make sure to place a noticeable banner stating that the feature will temporarily be unavailable
- You definitely want to make this prominent because it is immediately useful to the user unlike a survey that is pushed in your face with some websites.
Once the feature reaches the unavailability period then make sure that they can still access the page/widget but place a message about it's temporary unavailability.
You want to hold the user's hand throughout the entire process because you've already earned their trust in your product/feature and now it's time to act appropriately and maintain their trust through this process of change because people DO NOT like change.
I have done banking through Chase and used their online portal extensively. Regularly, they schedule maintenance and I am informed once I log in, they do not email me actually. A big, yellow, boxed message reads "ATTENTION: Service will be down for maintenance on Sunday, October 12th from 8am to 9pm EST. We apologize for the inconvenience."
I never checked but I think their login page will display that message as well if I were to visit on the maintenance day.