I started playing as a Necromancer (single-player, version 1.0.2) and encountered a similar situation: by the end of the 2nd week, a queue of 3 opponents with different flags formed outside my castle. They apparently made a truce among themselves, and their only goal was my hero. First, the AI Necromancer attacked. He already had a larger army than mine (10 Liches, 12 Death Knights, and I had 0 of each), but I managed to defend myself. Then, a Demon attacked – it was a hopeless battle. I'll try to replay, but it will be difficult to gather enough strength to fight two or three opponents simultaneously in one turn.