What will happen if they do not remove themselves from the pond, and starts as they are a pawn - they will just not bid in the first turn and fall out of the game.
If they are already playing a pond then turn into a pawn, then their last bid will just be repeated until they fall out (or win - which I think has happened once)
WellyWales: It should be pointed out that if a pawn falls in with zero in the first round, there will also be someone else fall in with the next lowest bid, but thats the first round only