Should I assume the Open Pit patch works like a permanent Create Pit spell? It doesn't say say but I'm assuming this how the patch was intended to work despite not mentioning the spell.
It would then otherwise would be logical to think that using the patch on any surface, horizontal in relation to gravity or not, would then literally destroy matter in the void that it has created. Possibly including creatures.
It's reasonable to assume that it works like Create Pit.
But, it would have to be placed on a horizontal surface. And if it functions as create pit it would not destroy anything. They might fall into the permanent extra dimensional space that has been created, but they wont be destroyed.