I disagree somewhat. The money doesn't matter yes, any possible delays should be discussed prior to beginning, yes also. BUT, if player B is called away player A can quit, leave, whatever he chooses. If he accepts the circumstances he can wait, but it's optional. He can quit and only agree to restart if he likes, too bad if player B doesn't like it.
Frankly, I think player B forfeited, but these things are unenforceable. He's not going to pay anyway. The general scenario brings up the gambler's code regarding quitting a winner. Who says that you have to play a loser until he's had enough and give him a chance to win his money back ? If I get tired or have other obligations I quit. I might play another day, I might not. Life is tough.
The TAR website sells a t-shirt with the logo, "I make my Mother post". Good idea. All this said and still, a gentleman would be understanding about player B and the match, but gamblers often are not gentlemen..Tom