I think it's safe to say that there's a lot of contention over what constitutes making a meaningful decision (vs fateful) and things like player agency. Jumping into a dark hole is probably fateful, but a lot of people would say it's not meaningful because it offers no sense of what the consequence will be so the apparent meaning of the decision to jump in is obscured. Thus the character doesn't really have full agency despite being in control of their PC the whole time.
That said, I'm in the camp that player agency does not require a full understanding of the implications of any decision being taken. In the OP case, the PCs knew that without intervention there would be a ritual performed over a dead body to raise him and that it would have some negative consequences for the dead guy's heir (delay of inheritance if nothing else) and were suspicious of the whole affair. I don't know why, if I were a player in that game, I would need more to make a decision in which I felt I was in full control of my PC, whether I decided to intervene or not.
I think that brings a little light onto the nuance of the issue. Also this is what I'm getting so far. (not specifically addressed to you)
Excuse me if I sound like stereo instructions.
Player agency doesn't matter (as much) if there are no meaningful consequences to be had by their actions/inaction.
Player agency doesn't require specific knowledge of potential consequences to be had by their actions/inactions, but
Player agency is best respected when knowledge of consequences can be inferred or discovered.
Real violation of agency is based on the relative degree of consequences/rewards caused by their actions/inactions, and further relative to a reasonable level of knowledge of consequence obtainable by the player prior.
In the case of the dark hole.
The player is exploring in a cave, and finds a hole. The dark hole appears to look like certain death. The player inspects the hole, throws down and torch, and it fades away into darkness. The player jumps head first and after a long fall dies upon impact.
(Knowledge) A dangerous non descript looking hole that appears to be almost bottomless. With no emerging reason to jump in.
(Action) The player jumps in.
(Consequence) The player falls hundreds of feet in darkness (having no magic to slow themselves, or otherwise slow their decent) impacts on the ground and dies.
In this case
(Knowledge) Shady noble wants body taken from crypt, later discovered to be necromantic in nature (Runes, skulls, blood, zombies).
(Action) Body is retrieved, and party follows noble.
(Consequence) Body is taken into another graveyard crypt
(Knowledge) Noble doesn't want people attending ritual, besides suspected evil cleric after being convinced.
(Action) Party waits outside while ritual is performed
(Consequence) Body is resurrected
(Knowledge) Dead father is walking out of crypt looking dismayed and quiet, noble is trying to shoo people off
(Action) Party takes money and leaves for Inn, and leaves the necromancer and his group of hooded figures to their business
(Consequence) Necromancer goes to family home and with their pact bound fathers help, slays/captures the family.
(Knowledge) ?? Paladin feels something is off? Feels guilty?
(Action) Goes to his church and confesses crime to high priest the next morning.
(Consequence) High priest consoles him and says he will go investigate the family.
(Knowledge) Family is discovered slain (father and son missing)
(Action) Paladin confesses to guard, and the diviner investigator wizards, and divulges ritual location.
(Consequence) Guard, and wizards use divination magic to investigate the ritual site and hunt down perpetrators (including the party)
Does this seem like a rational progression of events?
While I want situations to be mysterious at first, I never want to engage in whole heartedly into Shmuck bait