If a careless person were to disconnect one spark plug lead on a 4 cylinder engine to improve access for some maintenance work, and afterwards start the engine from cold and sit there thinking "hmm... that sounds a bit lumpy" for
30 seconds before realising their mistake and switching off, would that kill the catalytic convertor?
If it hasn't definitely killed it, what's the best way to avoid further damage? Leave it overnight to allow the petrol to evaporate?