Quality of life matters in most of these marginal cases. If they are going to give you the Konno procedure (scrape extra tissue out of a thickened ventricle), there's tons of things that can go wrong OTHER than death. Death is assured, either way, for everyone.
It depends what the outcome is without the surgery. If I'm dead without it, I want them to operate regardless. If there's only a chance of death, or the surgery is aiming to improve quality of life (rather than prevent [imminent] death), it's more of a judgement call.