I had to abandon a battle between Silvermaiden (me) vs Paragon Protector (enemy) as neither could hurt the other and PP added 15 shield to itself well before skulls ever became a threat. Retreating did’t seem like the right move, so I just shut down the game to get out of it. Maybe the devs could add a “Truce” button which would be available in scenarios such as these, unavailable otherwise.
I imagine there must be other pathological scenarios like this. Silvermaiden alone can be tough to finish off if you lack sufficient firepower. I’ve been in several battles this past week where the only reason I could finish her off was that I could time a death mark just as her mana was near zero.
Both of those count as a loss, so there’s no reason to shut the game down unless you did it for philosophical reasons. (Or you were attempting to short-circuit a long cascade, where you can’t exit until it’s done, but it takes longer to load the game after quitting than waiting it out anyway.)