Warlocks are not Clerics, they are not even Divine casters, and I definitely would not rule that the fiend/fey/Cthulu can revoke granted powers. They might seek to punish the Warlock in other ways, but PC-Elric can definitely act against the interests of patron-Arioch while retaining all abilities.
Divine casters such as Cleric & Paladin, I can imagine stripping them of power in some campaign settings, since in some worlds the power they serve can sever or reduce the strength of the link between character & themselves. The PC could turn to a new deity though & likely get powers restored. In other worlds the gods are remote and the Cleric can effectively do what he likes as long as he genuinely believes he's serving the deity's interests. In others the corrupt Cleric may think Pelor is granting him power when really it's coming from Zehir, CS Lewis style.
Divine casters such as Cleric & Paladin, I can imagine stripping them of power in some campaign settings, since in some worlds the power they serve can sever or reduce the strength of the link between character & themselves. The PC could turn to a new deity though & likely get powers restored. In other worlds the gods are remote and the Cleric can effectively do what he likes as long as he genuinely believes he's serving the deity's interests. In others the corrupt Cleric may think Pelor is granting him power when really it's coming from Zehir, CS Lewis style.
