After Salacia disables the Dethtank, Charles says "Engage Alfa Monstro." Alfa Monstro is a nickname for the Alfa Romeo SZ sports car, which had (among other things) a much larger engine than the other Alfa Romeos.
It makes sense Salacia is making a move personally to get Dethklok to stay together, even if it's in fear of him; he still needs them to make the song that will save the world.
Salacia is killing himself in a meta sense, since Roy is also voiced by Mark Hamill.