I just meant that lightgun games have been in decline for some time, from the hayday of Time Crisis 2, and when arcades tended to have three or four different lightgun games.
As for dead video game genres, sure it's practically impossible to name a genre that has truely died, but a few games over the years is anything but a thriving video game genre.
Also let it be known, I love lightgun games, Time Crisis 2 and Crisis Zone are some of my favorite arcade games of all time, just it would seem to me that the genre has sort of lost it's luster.
I tend not to buy lightgun peripherals only because I know there'll be a serious lack of content, especially content I haven't already beaten. (When there is only a handful of titles it doesn't take long to exhaust your supply.)
So in the end, I consider the lightgun game to be a dying breed, because if it was something that really interested the public, more developers would love to cash in and try to make some, and right now you get a few games from time to time. (Practically every other genre gets games at a more constant pace...even music games)
Though I hope lightgun games return! (And arcades...)