We need to take this back to basics and then rephrase the question.
Zen Cart operates on your server sending web pages to your visitor's browser. You want to take a particular action when the visitor leaves your site in their browser - but their browser won't tell Zen Cart this - it's off talking to some new site, or closed down.
What you need instead is a program that runs in their browser to detect that they're navigating away and ask these questions (and equally importantly collect the answers for you).
You could write this yourself, but most likely you'd want to use something that's already out there. Once you identify which best suits you purposes, your question becomes "How do I integrate xyz into my Zen cart site?" so that Zen Cart loads xyz in your visitor's browser along with the rest of your site.
There are a ton of feedback tools, I've only used one and that was from a specific client request so I'm not going to claim to know what's best generally, let along what's best for you. But this link may help you to find an appropriate one.