My Phoenix Died (really): How?

[tinkthank]

A fire-9 air-4 Phoenix was brooding in his capital of Marignon when a horde of trolls snatched a neighboring province from under his nose, fairly early in the game. That province had a positiv dominion of 1 (turn X).
So on turn X, he was given orders to fly in. (Scripted Mistform, Holy Pyre x4, spells.)
Turn X+1: Phoenix flies in, kills some trolls, but gets wiped out.
Dominion of said Province in Turn X+1 was also 1.
However, the Phoenix wasnt in his capital. He was dead. (As could be verified by the fact that all my priests in friendly provs had, and started to make use of, the option "Call God.")

I have only one explanation for this phenomenon, and I would like to know what others think of it, and what they think this means.
In that province there were stealthy enemy preachers. Turn X ended with Dominon of 1. Turn X+1 began, and "prayers" took effect, perhaps lowering the dominion to 0. (Note: it is really hard to tell, since the dominion-related HP of pretenders is hardly a good gauge of whether dominion is positive or not.) Then the battle ensued. Then "Dominion" took effect (I take that to mean that there was a temple check of some sort which pushed my dominion back up to 1.)

Could that have been it? If not, what else could it have been? And if so, does that mean that immortal units can still get iced much more easily than we think?

RECRUIT
RESEARCH
EMPOWERMENT
FORGE
RITUALS
MAGIC BATTLES
SEARCH
++++ PRAYERS +++++
BLOOD HUNT
LUCK
ASSASSINATIONS
FRIENDLY MOVEMENT
+++ MOVE BATTLES ++++
STORM CASTLE
ENCHANTMENTS
MAGIC ITEMS
SNEAK
BUILD
SPECIAL ORDERS
INCOME
STARVATION
UPKEEP
+++ DOMINION +++
SITE EFFECTS
HEAL
MERCS
SCOUTING