I would've thought it was the other way around. Fairchild doesn't seem to be doing too badly, to me. I haven't bought hardly anything from On Semi in the last forever. Probably a good combination though; Fairchild seems to rock with discretes, which I've hardly seen any from On Semi (aside from the old standbys like 2N3904s and MJE*'s). For what I know of their discrete and IC portfolios, it should be a good combination, though it'll probably lead to the obsolescence of some redundant parts.
Tim