Blood slaves?

[Executor]

The problem is I don't have many blood hunters, they are all lore masters with rare blood picks that have some boosters, so I always keep them on retreat in case of a attack so they don't get killed.
So I don't know what is better, to risk loosing some slaves on retreat or risk loosing rare lore masters with blood
I did try to put the slaves next to the mage, but they still act as regular troops, and don't get used for the spells