I am not sure afterscan on a checkbox would make sense as something to use in Form Logic. While I think it could work, it would be unusual in that you would need to be 'focused' on the checkbox and then 'tab' out of it which is not really a natural event on a mobile device.
A better option for tracking a checkbox clicked or not might be the "ValueChanged" event.
I am not as clear what you mean about "if a checkbox could be skipped altogether"?