[Red Badger]

What if the companion star was an even smaller star than the white dwarf? There might not be enough matter to start a nuclear explosion, and so the outer surface of the larger star becomes a shell of hydrogen and helium and that’s all that’s left of the companion.......................

[Nateman]

Thanks to gravity waves radiating energy the two stars will spiral together until they eventually collide. The gravitational energy of such a collision alone is enough to make such a collision quite spectacular.