Once a survey is published and users enter their data, can they fill some of the data in, leave the form and come back to it later?

I have a very lengthy questionnaire that users may want to complete over several sittings.  Is it possible for those filling in the questionnaire to begin a questionnaire, save the completed entries and come back to it at a later time?

You can follow our user guide  to achieve this.

User guide: How-to-Let-Users-Update-Their-Form-Submissions-at-a-Later-Date

As add on for better presentation you can also check this user guide: 

How-to-Change-the-Text-of-the-Edit-Link-in-Your-Email-Alerts