they are absolutely incorrect. they changed this. i dcd from a boost yesterday that 100pct got finished after i left. there is documentation and strikes that occur for depletes, regardless of reason. i specifically spoke to the advertiser and the staff and the run was still timed, in fact. i did not receive even gold in the mail for this run. i have also left countless runs this season due to underperformance, and a handful were completed without me, because i still got dungeon completion notifications. not a single one resulted in even gold.
they changed this either right before dragonflight, or at some point during the season without mentioning it. i run quite literally hundreds and hundreds of keys a season, and leave many keys early on, and would know if i was wrong about this one