How to deal with one of multiple clients not receiving an RPC call for whatever reason.

I'm curious as to what the best practice would be for something like this.

Say you were making a networked checkers game with spectators. The game has two players and a spectator.
Player A goes to move his piece from board space A to board space B and he communicates this to everyone else by sending an RPC.
What is the best way to ensure that all players received the RPC before making the move?
What do you do if Player A and the spectator get the RPC but Player B is having connection issues?

Thanks