Absolutely. An easy way to rebuild an army is by using a troll and evening and night or in the underground. You can constantly sacrifice him and he will regenerate each turn.
However, it will take an extremely powerful spell to manage to get a lvl 5 unit (lvl 3 sacrifice provides 60% of the sacrificed HP in troops, so you can imagine). For a cyclops, you need to sacrifice quite a bunch of points to get the HP he has.
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