Does Mr. Vinge ever mention what happened to the Qeng Ho during the events of A Fire Upon the Deep?
In A Fire Upon the Deep, the Qeng Ho only exists in Pham Nuwen's memory, which are known to be strongly influenced by Old One. Ravna hasn't heard of it, and Pham notes to her that
“So you looked through the Relay archives, and didn’t find my Qeng Ho.” My Qeng Ho. He paused. Remembering? Trying to remember? For an instant Ravna saw a gleam of panic on his face. Then it was gone, and there was just the lazy smile. “Can any of us imagine the archives of the Transcend, all the things Old One must know about humanity? Vrinimi Org should be grateful to Old One for explaining my origins; they could never have learned that by themselves.
“My own memories? (…) Yes, the Qeng Ho. Pham Nuwen, the great Trader of the Slowness. All the memories are still there. And for all I know, it’s all the Old One’s lie, an afternoon’s fraud to fool the Relayers.”
(We do know that the Qeng Ho did exist by author fiat, but that is not clearly said in-story — the biggest clue is that his knowledge of medieval technology and strategy turns out to be accurate. We know it from the author's notes, and from the existence of A Deepness in the Sky set in the same universe.)
It is known that
all humankind in the Beyond was descended from Nyjoran stock.
All evidence suggests that Nyjora was not founded by a Qeng Ho expedition. That's not something they remember, which would clash with the fact that humanity in Ravna's time does have histories dating from before Nyjora, going back all the way to Old Earth. Ravna even found a record of a Qeng Ho (?) “on Earth, a thousand years before space flight”. Ravna even states that “there must have been Asia-descended colonies”, but has no knowledge record of an actual one. Pham's physical characteristics (which are likely to be more accurate than his memories, as his DNA was presumably intact) don't match Nyjorans' (he has “bright reddish brown [hair], a color [Ravna] had only seen in pre-Nyjoran histories”). Human names in the Beyond are consistently of Norwegian inspiration, contrasting with Qeng Ho's Chinese streak.
We're told that Earth and the Qeng Ho volume are “thousands of light-years in the Slowness”. That would make escaping the Slow Zone a very unlikely event, barring major Zone surges that would leave a civilization in the Beyond for long enough to develop ultralight technology and expand. It's thus very plausible that apart from Pham's ship, Nyjorans were the only ones lucky enough to push in the right direction. Qeng Ho may be long dead, or it or its recognizable descendants may still be operating somewhere in the Slowness.