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That's a good and valid question. I've been thinking about it, and I've come to the conclusion that, yes, that's how it should be. Because there are resurrection spells (raise dead and return), so you need to manage to raise at least one unit before the last hit.
Let me clarify and elaborate on my position regarding the arena result.
The arena should simulate the main battle between the main heroes. And if both heroes disappear as a result of this battle, it means there were no winners. The only difference between the arena and a real battle is the absence of a very rare tactic that I could describe with the words of our footballer who scored a goal "...! ... to you, ...!": if one side has no real troops left, but only summoned ones, the second hero brazenly runs away and buys what he needs. And then the other hero disappears:))). This is a sneaky tactic, but it won't be practiced in the arena - the arena is the arena, and you can't run away or surrender from it.
Let me clarify and elaborate on my position regarding the arena result.
The arena should simulate the main battle between the main heroes. And if both heroes disappear as a result of this battle, it means there were no winners. The only difference between the arena and a real battle is the absence of a very rare tactic that I could describe with the words of our footballer who scored a goal "...! ... to you, ...!": if one side has no real troops left, but only summoned ones, the second hero brazenly runs away and buys what he needs. And then the other hero disappears:))). This is a sneaky tactic, but it won't be practiced in the arena - the arena is the arena, and you can't run away or surrender from it.

Орден Феникса – харизматический :) лидер