I ran auto all night without losing or crashing--
Killer Prime - Sacred/Warlord/Sustain
Max Cyborg - Valhalla/T3
Killer Beast - Starfire*
Prisoner - Sacred/Boost/Sustain
Usually about 1:30. The longest runs are about 3 minutes, but the outcome is inevitable.
...
*eta: 1st wave always passive disabled and perma-deathed, but IF Cyborg doesn't one-shot them, they wreck themselves on the Starfire while my whole team is stunned.