It would be the logical one many may say. If they did buy the Nymex, I am not sure how much higher of a bid it would justify. Since the buy out at this point in the Nymex price would be equivilent to the BOT buy out on the CME just made. If they paid more than $140 per share I would run like heck from ICE shares for the intermediate term until it worked itself out and one had a clearer picture of how the merger was working.
Bottom line (I could be wrong) the Nymex is just not worth the Risk/Reward at this current price, although I don't see much down side. Kind of a stalemate trade.
If you want to play this trade buy the CME or NYX.