Maintaining deletion discussions actively open after something is deleted would probably have the counter-intuitive result that fewer would be undeleted. At the very least, the heat would be reduced.
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I'm not so sure about that. Wouldn't it just attract people unhappy with the result piling up votes and requesting a recount of the original result? Having stuff undeleted isn't a bad thing, as long as there's a proper reason behind overruling the original AFD debate (new info, faulty closure, or lots of blanket votes).