Admittedly, saying that implies that it was alive at some point, which I'm not entirely sure of.
TBO obviously doesn't cover a whole lot of power metal, and there's a reason for that: it's a genre that's basically been circling itself since its inception. I enjoy some power metal (see my post on X-Japan,) but I openly consider it musical candy; I don't think that at any point Kaledon is going to change my life or views of art. This is not to say that power metal can't be artistic- merely that such examples are few and far between, and even within that tiny bracket usually a result of combining power metal with some other style of metal. Next to thrash, power metal is just about the most restrictive and infertile style of metal in the greater pantheon, but unlike thrash, power metal didn't have the useful transitional property of leading towards extreme metal. Power metal just sits and rots.
(As an aside, the transitional purpose of thrash was by far its most important quality, and it should probably have been forgotten completely after death and black metal consolidated themselves. The best thrash sounds a lot like death or black metal, and the further away from the extreme edge of the style it gets, the worse it tends to be.)
At this point a number of people will probably cry out that I'm not making a distinction between the US and Euro styles of power metal, but this is a false dichotomy since USPM shouldn't really be considered "power metal" anyway. USPM tends to just be an expanded and intensified version of Manowar (or, for those with higher opinions of themselves, Manilla Road or Cirith Ungol,) and really ends up just being heavy metal rather than "power metal." Of course, this is a matter of opinion also, since Euro power metal has never become substantially more than an expanded and intensified version of Iron Maiden with some influence from thrash's more aggressive rhythmic aspects. Of course, we can break it down further from there, with pop-metal like Sonata Arctica or halfhearted extreme metal experiments like Wintersun, but the answer seems fairly clear: when it comes to this discussion, USPM is fairly irrelevant since no one's listening to it anyway.
Much like thrash, power metal's development as a genre is hamstrung by a set of inherent restrictions to its construction. The reason why power metal hasn't evolved further is the same reason that blues is now ignored: when you can't break out of a certain structural limitation, stagnation is the only result. In power metal's case, it's a combination of several factors:
1. Dissonance is forbidden. Without the ability to really maneuver around the chromatic scale, and with power metal's over-reliance on major key melodies, the musical palette available to the genre is painfully limited. Dovetailing with this is the reliance on clean vocals- why, exactly, is Children of Bodom one of the only popular power metal bands to employ something a little harsher?
2. There's only one way to go- prog. While I despise hybridization for its own sake, I understand that it has its points, and power metal's hybridization is basically limited to prog and prog alone. While there are token instances of further diversion- power/death (Painmuseum,) power/black (Bal-Sagoth)- power metal tends to just go further and further down the rabbit hole into prog, which, ironically enough, just tends to restrict it further.
The other option is folk/power, which has produced one band worth investigating (Elvenking) and a lot of garbage.
3. Sheer laziness in riffcraft. This might be a minor point, but show me a goddamn power metal band these days with riffs that aren't remarkably similar sped-up Zao breakdowns.
I would provide a list of power metal bands that are doing something worthwhile, but I would prefer just to say that power metal is stupid and will probably never get better and consider them collateral damage.