You are the only Shortsale that they have to deal with; they probably have hundreds at a time.
And they don't care a twit about you, and they don't care a twit about your deal:
In fact, you are an imposition to their workday; you're something that they HAVE to do.
Either you will accept the extension request, or not! Either way.....
You are not going to spite them, or make them feel bad it you refuse, or ignore them.
Do you want to cut off your nose to spite your face?