The original clem will be fine. Severe pruning does nothing but help them sprout out more vines from the crown.

Agree with buyorse11888. I never tried rooting clematis stems-could work.

Rooting Clematis stems is extremely difficult and time consuming. You will have much better result if you will wait till your vines will grow back and layer them.

I agree with everyone - your son did not harm the Clematis. It will grow back in no time. Give it some fertilizer, mulch around to mark the location, and wait.

Been there, done that! lmao! Don't worry at all! They love that sort of thing! It'll just make for a stronger clem! You will see it start coming back in a few weeks if you look for new vines near the ground. ;)

Oh, and just keep watering it as if it was just fine! lol