Does Hold Person cast on a Spider Climbing NPC affect their ability stay on a vertical surface?


An NPC spell caster that is using spider climb at the top of a 30′ pillar where it meets the ceiling is magically held by hold person. I have two related questions:

  1. When Hold Person goes into effect, does the NPC fall, or does the Spider Climb magic (which is still in effect) keep his hands and feet bound to the pillar and leaving him suspended 30′ off the floor?

  2. Assuming he does not fall immediately, if the party shoots him with an arrow or other ranged attack, since Dex checks auto-fail when Paralyzed, would that knock him off (and thus fall for 3d6 damage).