Obsidian probably didn't want to re-use characters, so it doesn't really touch on it. But that Rodian weapons guy is back, and much of the Khoonda Militia is made up of Dantooine inhabitants, plus there was mention that the Matales vacated their mansion AFTER the Malak attack.
As for Taris, again, yes I'm sure the vast majority of the population was killed. However, since the planet itself was not destroyed, I'm sure a small percentage of it would have survived. That's not only possible, but also quite plausible.