Well, I guess it comes down to how badly you want to play DK. From a dust perspective, this has less value than the mini-sets (just over 2k dust for Path of Arthas versus like 2500 something for the mini set). The mini set is often a good value as well because the cards usually catch some nerfs giving even more dust value. Right now, it's looking like DK isn't particularly overpowered. It might even be straight up bad, but we'll see. In fact the entire expansion isn't looking very impactful. Usually, when that's happened in the past, you can expect Bliz to go back and buff some of the new stuff and nerf the old. As such, I wouldn't expect at this time to be seeing any full dust refunds off of Path of Arthas cards.
For me, I just opened the packs. I'm sitting on something like 70k in dust. I'd rather spend the gold on packs that have the potential to be more universally useful than a bunch of cards for a class that I may or may not end up playing. And if I really need it to, I can just spend some dust to craft a Path of Arthas card. However, if one of the legendary cards in the set does catch a nerf, I'll probably buy the set for the dust value if it's still available.