This is called " Wet Stacking " or " Slobbering ". Diesels pump a lot of air through the cylinders at idle, this cools the combustion chamber.

Soot is so fine so it causes more of a long term wear issue than rapid failure. I don't think that diesel fuel diluted oil ( reduced lubrication quality ) would cause a bearing to fail on it's own at idle. I do see idle oil pressures being reduced and coupled with increased bearing clearances due to wear contributing to the failure.