They aren't holding their coins, so all sales immediately create a supply in bitcoin. This could cause a temporary price drop if sales are high enough. I doubt this is much cause for concern although.
What would happen to bitcoin if the planet for some astronomically small chance got a world wide power outage for a day? Would the network and block chain survive such crash or would everything get irreversibly messed up?
The only way this could happen is by a solar flare and then we'd have more things to worry about, for instance that all electronic devices just got fried.