Yes I did read a post on IRC about the many outs in the agreement, I have not read the agreement in detailed. But if I was NST or KCGM I would prefer to take over the merged entity - it is a much more neater transaction and scalable transaction, on the proviso that Horizon mining is not re-rated by the market.
Put it this way.... If another compelling offer did come along - you be nuts to enter an agreement that would lock yourself out it.