How can I render the form unable to be used while keeping the form available in the background?

I sent my form link to many people with a deadline date to submit their responses.  I would like the link to become unavailable to everyone after a certain date while keeping my application live for future use.

You can use the form Expiration Limit feature to achieve this.

User guide: -How-to-Limit-Submissions-in-a-Form

When Expiration Date is met, the form will be in disabled status. 

You can just enable again the form anytime.

User guide: -How-to-clear-your-form-expiration-s-date

Thanks.