Well, that may be true scientifically, but the point of the fire analogy is not this. The point is not that the fire (and whatever it metaphorically represents) somehow still exist. When a fire goes out the idea is that it totally ceases. Otherwise the Buddha would not use this famous metaphor for the cessation of craving. Craving totally stops existing at nibbana, I think you’ll agree.
Likewise, in the Upasiva verses the going out of the flame also means cessation, although here it refers to parinibbana, the cessation of the aggregates at death.
There are quite a few, though, most notably AN9.34.
Venerable Sariputta addressed the mendicants: “Reverends, this extinguishment (nibbana) is ease!”
Then Reverend Udayi asked him: “But, reverend Sariputta, what ease is there when nothing is experienced?”
“Then exactly that, reverend, is the ease: that nothing is experienced.”
I know you will probably argue that “feeling” and “experiencing” mean something different, but the dictionaries suggest “experience” for the verb forms, including vedayita which we have here.
Vedayita and veditabba are two forms of the same verb, vedeti, which means to feel, experience, know, or understand.
(source)
So when you don’t feel anything, you don’t experience anything. You can translate the verb either way. Some translate even the noun vedana as ‘experience’, including Warder (of the famous Pali grammar book) in his Indian Buddhism.
Anyway, our discussion is getting a bit beyond the scope of the essay, so I’ll probably leave it at this.