COT falls down when scrutinized, but I like the episode, anyway.
Regarding the survival of the Dax symbiont, there may have been a male Trill on the Defiant when it crashed. He and Jadzia could have started a full-blooded Trill line specifically for the safe future transfer of Dax.
Of course at some point there would have been some in-breeding but that's something I'd rather not think about so soon after lunch.
It's a safe bet that Worf was the only Klingon aboard, so all of the ridged humanoids we saw were at most Half-Klingon. Also, keeping in mind that Klingons live longer than humans, they may have gone through fewer generations than the others so their line would have been closer to the original.