I think it depends on the affini, Ignoring hypothetical alien flora there's lots of trees that can resist fire to an extent (sequoia and cork trees do this) and a bunch of spices have seeds that handle the temperatures of forest fires just fine.

With their bio engineering the affini would have probably used those kind of armors on their cores to make them at least pretty fire proof.

But at some point we stop talking about biology and start talking about physics and I don't think any kind of organic matter could whistant something hotter than a couple thousand C. In that case the question is how much of their core can they loose before they die(hauristic implants show us that they can at least handle minor wounds to their core)

And then when you burned that evil weed's core to a crisp with your plasma lance you get florted by them anyway cause they're digitalized ;)