It is essentially like going afk to get a sandwich while you are in the middle of a match in TF2 or something. One turn isn't going to make or break the game, and everyone gets to keep playing. As long as we make sure to send a friendly reminder to the AFKers, then I don't see how this ruins anything.
Also, if the team you bet your money on has someone that goes AFK all the time, sucks for you, you placed a bad bet. Thats gambling.
And people can still technically win if someone never moves, it just isn't as easy. If Leroy wants to he can just put a reward multiplier on any team that has someone drop early on. If he wants. If not... meh.