Edit on my last message : the first screenshot is to prevent default back-button behavior on Android. For swipe-back gesture on iOS, just consider the second screenshot.
Now, swipe left to close is handled on native code.
How to add Exit button on AR View.? click on that button, will close AR View.
you do have access to the native files of the Wikitude Cordova plugin; so you should be able to change the behaviour an way you see fit.