Dave: I believe the poskim only “scrap” it depending on the method of suicide. If the method of suicide didn’t cause instant death, we assume he did teshuva before dying even though he was longer able to prevent himself from dying. If he caused the death instantaneously, there was no time for teshuva.
We use the assumption for teshuva to determine how to treat him post-death. Obviously Hashem knows whether there really was teshuva for how he is treated in Beis Din shel Maaleh.