Had a run where the game just robbed me of a win. I had killed the boss, but due to running a basically 0 dps 2x T2 Footman 1x T2 Cleric 1x T1 Cleric setup. The adds were still alive. So I had a single living Footman sitting in the middle of the orcs slowly killing them. With enough sustain that he was immortal. Then the "Run Ended" screen popped up. But the fight continued and my trustly single Footman eventually killed all the orcs. But I'm guessing it still didn't count as a win.
I guess that's a more futureproof way to do it. Currently the end boss doesn't have any sustain, so a soft lock isn't possible. Which means you don't really *need* the timeout, and could just remove it. But I'm guessing that would cause issues on other/future bosses that may just be able soft lock you with sustain.