I think a lot of the competitors at EBR and RMAC are shifting from .22 and .30 to .25 King Heavy. I recently shifted from .22 RDM to .25 King Heavy, and others like John Bagakis and Thayne Simmons also have switched, either from .22 or from .30. I know of a few other top shooters that are also switching. The .22 RDMs have a similar but slightly less BC, but the pellet quality isn't what it used to be. The .30 caliber pellets are good, and very predictable in the wind, but have a noticeably lower BC and move more in the wind than the .25 King Heavy. Plus the .25 King Heavy can be shot at a higher speed (like the RDMs) compared to .30 pellets. I'm shooting my .25 Red Wolf HP at about 960 to 965 FPS with the King Heavy pellets...
So, no, .25 caliber isn't dying as far as I can tell...