National Australia Bank announced yesterday that its transaction agreement with Axa SA to purchase Axa Asia Pacific had been terminated.The move follows the announcement by the Australian Competition and Consumer Commission that it would oppose the merger of NAB and Axa in the Australian market.The announcement has prompted speculation, reported by Bloomberg, that AMP will make a revised $6 a share bid for Axa.NAB was offering $6.43 a share for Axa, while in December AMP had made a cash and share offer worth the equivalent of $6.22. The Australian this morning points out that AMP's share price has fallen since then and the value of its offer today is $5.42 a share. The Axa Asia Pacific board is unlikely to accept an offer that low but AMP is certainly not going near the $6.43 a share NAB was prepared to pay.The window of opportunity might now be closed.