Hi Jake. As you describe, when changes in your survey force an underlying schema change (add new questions, change question types etc) Survey123 Connect for ArcGIS will delete your existing feature service and replace it with one that matches your new schema. This is the default behavior when the underlying feature service was originally created by Survey123 Connect. It may be possible to handle some additional situations (such as adding questions) where we could avoid the deletion of your feature service, but we will need to explore a bit more on that one.
The best way to protect your feature service from the behavior above is to use the submission_url setting. When you set this setting, the underlying feature service will NEVER be deleted by Survey123 Connect for ArcGIS. Instead, you will be responsible for making the necessary changes to keep your feature service schema matching the questions in your survey. To your example, if you add extra questions, Connect will not let you publish the survey again unless you add the corresponding fields in your feature service.
You can for example start by publishing your survey first. This will create your initial feature service. Immediately after, you would take the URL of your newly created feature service and then you would set it as your submission_url.
As described at the bottom of this blog post, we are working on improvements to the whole submission_url experience in our 1.10 release, which we tentatively release before the end of the year. If you are working with submission_url I would strongly recommend that you wait for the 1.10 release.
