Realistically, as soon as the 779 was mooted, the 748 was dead in the water. The 779 is roughly the same length, has a slightly wider wingspan and is only slightly narrower (and can accommodate 10 abreast in Y class - something I hope CX doesn't avail of, but suspect it will!); it really does much the same job as the 748, with two engines.
It's pretty much a no-brainer.
The only question is "when"; I'd expect an order before the end of the year. The A388 won't happen; the A389 may happen, but Airbus is in no hurry to launch it.