There is no such thing as a free lunch. I think any patron with the possible exception of The Old Ones would outright take away power from a warlock for what it deemed as misbehavior. Demons & Devils are under no game obligation to play fair with a PC at all and even fey as written in most old literature are extremely mercurial. Friendly one moment, desiring to cut your throat the next then completely indifferent a few days later. (Think of most characters in Alice in Wonderland). I give the Great Old Ones more of a pass because if they adapted from Lovecraft they may kill, ignore or treat with you. They are so alien that their behavior makes as much sense to us as we do to insects. There just is no way to describe them in tangible human terms. But especially fiends are known for corrupting and killing mortals. Going against their aims of spreading tyranny or chaos and evil would certainly cause them to revoke powers granted and if not possible completely block advancement in the future.