"N admitted he bid 4♠ using the UI"
Fair enough, but... The information that South thinks that North's 2
♦ was multi is extraneous. What is unauthorized to North is any
inference from that extraneous information (EI) that demonstrably could suggest a call or play. So when South bid 3
♦, what inference did north take from the EI about the meaning of 3
♦? How did whatever that inference was suggest bidding 4
♠? (See below).
It's been a long time since I played Benji, but it seems to me 3
♦ would be some kind of positive response, suggesting that there may be a slam somewhere if they can find a fit. So what would North do absent UI? Seems clear he would bid 3
♠, and that he bid four because he was afraid South would pass. So North failed to "carefully avoid taking advantage" of the inference that led to that fear.
Would South bid again if North bid 3
♠? Hard to say, in the circumstances, but I would expect not.
If South has UI before bidding 3
♦ then we have to ask what the LAs to 3
♦ are. Will the UI suggest to South that North's 2
♦ is Benji? I suppose it could. It could suggest that 2
♦ is a weak two. In the latter case, it seems to me that South's LAs might be pass (highly unlikely), and any number of diamonds up to five, with three (hoping to get out cheaply) and five (based on LOTT) as most likely. If the UI suggests 2
♦ is Benji, what are the LAs? Pass is not - 2
♦ is forcing. I suppose playing Benji 3
♦ is a possibility. Is there an alternative? Perhaps 5
♦. It seems to me that if South has UI from North's reaction to his announcement, the score should be adjusted to 5
♦, perhaps doubled, making however many it makes (or doesn't make).
If South
doesn't have UI, then 3
♦ stands, and now we consider what might have happened had North known of and acted upon his obligations. In that case, it seems adjusting to 3
♠ making however many it makes (4?) is appropriate.
The director should make sure that both North and South (next time the director sees him) understand their obligations in the presence of UI, the impact of the law in MI cases, and the proper way to alert partner's calls. He may also owe the table an apology for not being available when he was first called.
Penalize South for leaving quickly? I don't think so. He had good reason, it seems, and no instruction from the director to stick around. As for that making things more difficult for the TD, so what? What would the TD have done if South had had a heart attack? The director would still not be able to ask South anything, so that would be unchanged. I don't think
anyone would suggest penalizing South in that circumstance. At least, I hope not.