When I started one of the questions I asked myself was "What if a character becomes so popular the fans don't want them to die, but I run out of stories?"
The same thing happened to Conan Doyle after he killed Holmes, the fans appealed to bring him back and Doyle relented to pressure.
The other side of the coin came from a character in the Stephen King story "Misery," where the writer killed a popular character and while on holiday had an accident and ended in the "tender care" of his biggest fan, who said if her favourite wasn't restored the writer would die.
I thought I might have had the problem with either Patti or Mark as they both had great on line following, but sales never came from the books, so, I guess it became a moot argument.
Another question asked is how do you feel about killing off a character?
This has two parts to the same answer, firstly is the character selling your stories -- in the above instances, no -- as that is part of their existence. Secondly, although I do feel a certain sadness at their death, I would rather let them rest in peace than have a lingering death and I think two years for Ms. Canella with no sales qualifies as lingering and Mr. Johnson is not far behind her.