All of you that have red Dune, a Frank Herbert book, sciencefiction, sure,
but a lot of things more.
That saga (6 books) can't be conteined in the definition of sciencefiction.
But this is not the problem.

I want to answer the problem of returnig from the dead in a way similar to
that used in that saga.

For all that don't know much about it I want to say that a great effort by
the writer was devoted to balance the relations between tha powers involve
in all the universe.

So Herbet is a great exemple of a study about the balance between power in
general.

A gret power involved: the Bene Gesserit, own since centuries the power of
manipulating their chemical structure and became "immune to olding". This
power is formed by "witch", all women that kown the power of their mind and
their body in a super way.

The point is that all the Mothers at the head of this group have this power,
to manipulate their chemical, but they don't use this power because they are
aware of the chaos that is sure to blast the universe, cause inevitabilly
the people will kown about this, with some women that last for centuries
without aging.

I don't really think that all of us, role player, who use so easly the
powers to raise the dead, have wondered about the consequence of such an act.

I don't mean that I do this in my campaigns, I'm only wandering if not the
case but... don't you think realistic that the small elite who can win the
greatest human enemy, the dead, would guard that power from spare around.
Maybe is realistic that that was a secret, a supercontrolled secret. Maybe
they use that power only in a rare case. Maybe the PCs can discover that
knowledge during games.

Anyway, if you let you priests easly raise deads don't you think that
everyone who has the strenght to do this will look for a personal priest and
will force him to do the spell to raise him. Maybe a friend wizard can cast
a curse if the priest don't manteign his word. And yes, there are a lot of
courageus priests who prefer dying to use their spells forced, but a king
has time and resource, and at last he will find someone disposed or the way
to force someone.

The point is, all great king use this method, there aren't anymore dead king
(yes, sometimes their plane can fall and they will die, but at last a lot of
them will survive)

There aren't anymore descendent, family line and, mostly important

Birthright.

Let me know if you find a fallness or two in this elucubration.
Nadastor, Wizard of the Black Robes
"The power of a man is not in his hands, but in his eyes !
His life is not into his body, but into his mind !
The world is not around him, but is in him !"