If it's true that ATI's 80nm refreshes to x1300 and x1600 are delayed until Autumn, and nVidia really does release a Geforce 7950GX2 and Geforce 7900GS next week, and x1800XT really is replaced by x1900GT, then I think ATI will slightly continue to fall in the midrange segment. Highend, they'll combat alright with x1900, even if Geforce 7950GX2 is the fastest (pricing and availability will be a factor, though).
In other words, according to the recent report by Jon Peddie, where in the discrete market, ATI is holding 45% marketshare vs. 53% nVidia, I forsee it possibly becoming 44% ATI and 54% nVidia by Autumn. I won't try to predict past that point.
(Keep in mind, I'm not an analyst or anything; this is just my personal speculation. And it's also only an observation for the discrete GPU market.)