As another very useful and informative post about
Lootspots and Lootspot Etiquette put it:
Speaking personally, I rarely specify 'fast general', but if I have advertised a spot as 'ready to finish', then I will wait for a looter's general to appear, whisper that they have arrived and give them some time to respond and/or send attack. If neither of those things happen within a reasonable period of time then I will send them another whisper giving them a deadline by which time I will finish the adventure without them with no refund.
A "reasonable period of time" very much depends on specifics of the situation. For example, I am inclined to be more patient with a guild mate or a friend I have interacted with several times before than I am with someone I have just met for the first time, say, after an advertisement in trade. Usually, though, I just consider how much time it takes me to deal with any of the things that have called me away in similar circumstances, such as an urgent need for a bathroom break, an unexpected telephone call, a delivery at the door, one of the dogs throwing up... then I add on an extra few minutes for good measure, then send them the warning that I am going to finish without them soon.
Regardless of the situation, though, on the few occasions I have reached the point where I felt the need to finish without them, I have not given refunds. As far as I am concerned, if they were not ready to play, then they should not have accepted the spot or, if something unexpected called them away, that is their problem and I do not see why I should lose out because of circumstances beyond my control.