If you can not reload a save before entering the castle, or do not want to, there are health and mana shrines which refill themselves, so you can keep running back to them.
If you have enough scorpions, you can run into a group, release one and run away. If you do not cast Aura of Command, you can let it wander around killing things while you wait a safe distance away.
Otherwise, you can simply run for the exit (to the far west). If you have any shadow potions or statuettes, they can help (if you washed the dishes in the castle, the cook would have given you a shadow potion).
Help! Can't find Gyrion... Iona's dungeon maps (Spoilers)
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