Our fair play policy warns against this type of behavior. If a player habitually stalls, disconnects, or aborts games their account is restricted. There is more information here:
http://support.chess.com/Knowledgebase/Article/View/171/0/fair-play-policy
If a player stops playing, whether they have a substantial advantage, or can't win, they should resign. I had a player, (please no naming or shaming others on Chess.com)
who did that. I couldn't start another match, until this game timed out(12minutes). I sent a chat offering a draw and they didn't answer. If this player repeats , then they should be suspended for some time