Name: Angelic Pact
Circles: Life / Protection (or maybe just Life, as a Tier 9 spell)
Description: Every time one of your unit is killed in battle, it respawns in your summoning circle at the end of the battle. You must pay a mana cost equal to the unit's building or summoning cost, if you can't pay, the unit isn't respawned. The unit keeps its experience points and special abilities (like magical weapons if it was built in a city with an alchemist guild) but loses all unit enchantements and items.

I like the spell but would not place it in Tier 9 with the extreme cost and lost of items.
To make it Tier 9 I'd say the items stay for sure and maybe the respawn cost is reduced some. Also it would need a confirmation for each unit.