It is not expressly stated in the spell description of "Excommunication" that there is also a loss of Stability involved.
I am aware that the wording is probably not how you play it anyway, but I thought I'd bring it up. *cough*
Also, the estates of Viscount Nathal used to pay tribute of both gold and regency. - Am I to interpret that PETG taking them over has specifically seized to pay this tribute? - I would expect the holdings to continue as they always have, until ordered to do otherwise.
What description are you looking at, Niels? The Regent Guide v3.5 states:
Target provinces suffer a –3 penalty to prosperity, and the targeted domain suffers a –2 penalty to stability (provided that the Court province is one of those covered by the spell).
In addition, each of the caster’s temple holdings must immediately conduct a free contest domain (costing no GBs to initiate) action against any one holding belonging to the target regent (provided there are any in that province). Normal modifiers apply, and both sides can spend influence normally.
During subsequent turns target provinces suffer an additional –2 penalty to prosperity and the contest action must be repeated. The caster cannot voluntarily cancel the spell.
The caster must pay an additional number of RPs per province equal to the difference in target province level and his holding level. Example: Casting Excommunicate in a province (6), where the caster has a temple (4), costs an additional 6-4 = 2 RPs.
Character Level Equivalent: None. A regent that is targeted by this spell can limit its effects with a successful Will save (modified by stability). The spell is fairly focused, so the DC of the Will save is increased by 5. If the save is successful, the initial prosperity modifier is –2 (for all affected provinces) and the stability penalty becomes –1. A new save can be attempted during subsequent turns, and if successfully the prosperity modifier for that turn is reduced to –1.