Exactly 1000 – no, it’s not possible. Only if it’s a player, and they are in no more than 3 stacks, all gathered in one place. This is practically impossible, so there’s no point in considering such a situation.
The AI against a single Imp will divide the Archangels into 7 stacks.

But a smaller number is possible, in which case:

1. It must be in a castle, and tactics must be used. So that the turrets shoot first. In all other cases, the Archangels go first.
2. There must be a VERY strong mage, with expert Earth magic and the Summon Elemental spell (preferably also Earth).
We summon elementals from the first turn; there should be enough of them so that the Archangels don’t kill them in one turn. The Imp will naturally be killed; the number of elementals increases with each turn, and there are fewer and fewer Archangels.
Before killing the last Archangel, we resurrect the Imp (because otherwise, the elementals will disappear, and the defending hero will also die).