You might wan't to disable surveys from collecting feedback without having to delete the survey (as deleting a survey also deletes the collected responses).
1. To do this go to "Collect" and then "Surveys" tab and choose the survey you would like to deactivate
2. Under each question there is a bar with the option "% of respondents will see this question"
3. Set the bar to 0% in each question of your survey by clicking on the name of the question one by one, and the scrolling the bar to the bottom until it says "0% of respondents will see this question"
4. Add a text saying your survey has ended to the "end of the survey" view (the last view of each survey, as this will still be visible to anyone who might open the survey. This way they will know that the survey is no longer active
5. When you have set the percentage to 0% for each question click on the "Save" icon at the upper right corner of the survey and you are all set