I was playing a warlock, warlock, sacrificial priest and warlock team.
All the warlocks were dead, and the sacrificial priest used the sacrifice ability on himself.
This triggered the 30% chance to summon abhorath, who appeared in slot 1.
Yet I still lost, as you can see in the following screenshot:
I was expecting the fight to continue, as I still had 1 card…
On a funny side note, I also had it happen that sacrificing myself (last guy standing) also killed all the other player’s cards, and I won with no cards left