I am not entirely sure if I can add pictures or how to do so, but I have screenshots of an hour long stalemate I found myself in. Entering the spirit keep to farm some potions, I found myself at stage 10. Three of my team had died by the second minute, but I have Sniper, 6* ascended and level 42, wearing 4 pieces of the life steal set. Of course the Spirit Keep boss regenerates 50% of her health at the beginning of each turn. With only one Champion, I couldn't deal enough damage to depleat it below half, but did enough damage that it always replenished my own Champions health. An hour into the battle, I figured I would message my partner and tell him (also an avid Raid player), unfortunately rather than the game pausing, the app had restarted and thus the battle ended. So I never got to see how long the battle could actually last. 

Just a little story I thought you'd all might find a little entertaining.