I'm really surprised that I learned about this seal through THIS post and not elsewhere. And the question is a really, really good one.

I'm not someone who agrees at all with the minimalist approach undertaken by Copenhagen, et al. and I'd imagine that this find is going to make things even more difficult for them. (For those who don't know, the Copenhagen/Sheffield schools suggest (by and large) that the biblical text was a product of late antiquity and that none of it hails from legitimate, pre-exilic contexts. They tend to liken David to King Arthur.)

This seal comes from a provenanced context, the script seems legit, and the iconography is not surprising. I'll say this, too, that the Copenhagen school found a way (as unconvincing as it is) to read the Tel Dan Stele as "chamber pot" instead of "House of David." So, don't be surprised if they go through some mental and logical backflips to make this find fit their historical paradigm as well.

The fact of the matter is that we have Neo-Assyrian annals that cite Hezekiah and record his interactions with Sennacherib (see the Taylor Prism). I would imagine that they will approach this seal in the same way they approach those archaeological/textual data. If someone has a citation here as to how they approach those data, I'd greatly appreciate it. I've never actually looked at how they approach extra-biblical materials.

The thing with the Copenhagen school is that they're like your crazy uncle who shows up to Thanksgiving and says really, really absurd things. You kind of wish he had stayed at home, but are forced to acknowledge him because you're a kind human being and he's family.