The creature thrashes about violently as its webbing is ripped apart. The shimmer fades from the bridge's threads. In the distance, the cosmic array of lights winks out of existence, star by star. The spider's pained screech is deafening. You're not sure if it would be possible to kill a creature such as this, but you have done more harm to it in destroying its life's work than you could have ever done with bullets and blades.
As the woven threads of spider silk unravel, this realm's many suspended platforms of rock crumble and collapse into the endless aether below. You struggle to find something to stand on or grab hold of. Without the support of the web-bridge, the entire dimension collapses all around you.
With a final desperate screech that echoes throughout this world between worlds, Atlach-Nacha plunges into the eternal darkness below. You are quick to follow.