I also agree. Don't forget most are not aware that they are getting their powers from 'elsewhere' so although their Gods have gone silent
The vast overwhelming majority are still getting their powers from the same source they always have, their god from their plane..
Correct me if I am mistaken, but doesn't Ravenloft canon state priests receive their spells from some 'unknown' source from Ravenloft, since no god or goddess may enter, though priests may still believe it is their gods granting them said spells?
No. Your cleric still receives the magic from his patron. The patron still knows 'whats up' as well. But they CANNOT intervene, send visions, etc. when the follower is... being untrue. If you are aware of the Bible, the '
Book of Job' is essentially what clerics go through. The Dark Powers are basically watching if Clerics will remain faithful without God holding their hand. This goes for both native (and likley not real, or 100% heretical versions) and "foreign" faiths. The only time to the DP's come in the picture is when the cleric has 'fallen' they have corrupted their faith, in a way, where they do not feel they have violated their oaths or tenants (which makes them lose their spells, need to atone). This comes into play with very weak gods (demi-powers and below), dead gods, and a God does know when you have broken your vows, but as said, they can't come in to warn/punish you. It is up to your faith alone.
tl;dr FAITH IS THE MOST IMPORTANT THING IN RAVENLOFT, THE TEST OF THE FAITHFUL IS BELIEF DESPITE NOT HAVING DIRECT GUIDANCE OR PROOF, AKA 'PURE FAITH', CLERICS WHO STRAY FROM THIS EITHER FALL TO THEIR OWN DELUSION AND ARE SUPPLANTED BY THE DARK POWERS, OR GIVE UP/CRISIS OF FAITH/DIE/WHATEVER
also: YOU DO NOT KNOW THAT YOUR GOD KNOWS WHAT YOU ARE DOING, THAT IS THE POINT OF THE UNSPOKEN PACT, SEE
BOOK OF JOB