Considering the Iconians were best known for their gateway technology, we could assume some of them might have survived. It's hard to believe with such a technology, ever single one of them was destroyed.
There's this from Memory Alpha
It was speculated that not all of the Iconians perished in the attacks, but rather used their gateways to escape to other worlds. Indeed, the similarity between the Iconian language and the later languages of Dewan, Dinasian, and Iccobar has been cited as evidence of this theory. (TNG: "Contagion"; DS9: "To the Death"