While the overall point may be right, I have questions about some of the exegesis:
On eternal fire: It may well be that "eternal destruction" is destruction that is permanent, rather than that it is going on forever, but some of the references he cited don't fit his exegesis, even if their overall picture is consistent with his opinion. I believe the passage he cited about Sodom, as well as Jer 66:24, show that the fire continues forever even though the people or bodies have been destroyed, as an eternal sign of their destruction. This is, of course hyperbole, since in both cases the fires aren't still there. Thoses passages don't use the term "eternal destruction," and eternal refers (hyperbolicaly) to an actual thing, not to the finality of the destruction.
Eternal destruction itself occurs only in 2 Thes 1:9, as far as I can tell. Given 2 Thes 2:8 and 5:3 it is quite plausible that it refers to annihilation. That's how FF Bruce's commentary understands it. It may be how Calvin understands it as well: "the influence of that death will never cease," though the context makes it a bit less clear.
But that explanation isn't as obvious for Matthew's eternal punishment. Given the background of 1st Cent Judaism, which actually did think some people would be punished forever, that's at least a possible understanding of Matthew. Note however Matthew's references elsewhere to people being in the outer darkness, with weeping and gnashing of teeth (probably meaning frustration). That suggests exclusion from the Kingdom, but not being tortured by God. Is that the same thing as eternal punishment, or are some people damned and others frustrated that they didn't get a greater reward than they did because of their lack of faithfulness? I don't think we know for sure.
Oddly, Calvin doesn't really comment on the nature of the punishment in Mat 25:46. The closest he comes is "To destroy this self-complacency, our Lord gives them warning, that they will one day feel—but when it will be too late—what they do not now deign to consider, that those who are now so greatly despised are not less esteemed by Christ than his own members." On Mat 8:12 he makes a comment that I believe is consistent with his overall theology: hell isn't literal fire. It is "dreadful anguish, which can neither be expressed nor conceived in this life," because of being excluded from the Kingdom.