Some plants don't react well to topping. I have had mutated plants happen from topping, but I have never heard of a plant dying from topping. Did you do a hack job or more than one cut?

Topping a plant should be used with very sharp snips, in one, quick cut. If you used dull snips or hacked it up, you may sent it into a death shock or something, but I have never heard of a plant dying from getting topped.

Bummer man.