Existing A330 customers will probably pick the A350, but 757/767/777 customers (like JL, NH, SQ, UA, AA, DL, CO, BA, SQ) will stick with the 7E7.

Also, the 7E7 is supposed to be a few tens of millions cheaper (at least comparing expected list price to expected list price) and will be the better plane, since it won't be a "refresh" like the A350 is, but will be a "ground-up" new design (same reason the A330 was a better plane then the 767-300/400).

So Airbus will no doubt sell hundreds of A350s and Boeing will sell thousands of 7E7s and both companies will keep their respective "locked-in" customers locked-in. Airbus will continue to be denied the Japanese market (since JL and NH will remain Boeing - and therefore 7E7 - customers), but China is plenty big and if US survives, they can sell A350s to them, as well as NW.