When the forced play of a penalty card happens to be the best defence?
Would be interested in opinions on the following. The contract is 4S and declarer's RHO revokes, ruffing a diamond when holding a winning King of diamonds in her hand. The revoke is discovered before the next lead, so not established, and the defender substitutes the King thereby winning the trick. There is no advantage in declarer changing his played card. The defender's small trump becomes a major penalty card and is therefore led to the next trick.
The contract is -1 and at the end declarer remarks that if the trump is not led the contract would have made. This was I think incorrect but it got me thinking. What if the enforced lead of a penalty card is in fact the only way to defeat a contract, especially if it looks an unlikely play or was not found by most of the room? Would the director be right to use law 12B1 to adjust the score? It seems to me difficult because there is no way of telling what the lead might have been without the infraction. Is it worth asking the defender "what would you have led were it not for the penalty card"?