Divinity's Reach [PoF Spoilers]

With Balthazar dead and no new god of fire coming to take his place, what will become of the Balthazar plaza and roads in Divinity's reach?

If you're talking in terms of lore only, it's difficult to say.

I imagine such a decision would be made with Queen Jennah, the ministers et al on what they wish to do with it.

No-one knows who Balthazar's replacement is, if he indeed has one at the moment and with Kasmeer knowing the Gods have left, it's entirely possible they'd never know, so they can't carve statues or name it after an unknown God.

It would also depend on how much unrest the district was causing for the citizens - those whose family possibly died in the Crystal Desert or those who are so devoted that they believe Balthazar did the right thing and was unjustly killed. It would cause civil unrest by either keeping it or remaking it into something else for many reasons.

It may be something they touch on in season 4.

If the question is related to gameplay, though, very little at all will change. The maps at launch are effectively 'locked in time' so it'll probably remain exactly as it is in the open world.