This came up in a recent Dreamlands game. If Yog Sothoth moves into a territory where the Bhole is present, he is destroyed, but does he fulfill Opener's spellbook requirement for sharing a territory with an enemy Great Old One?
As far as I know the bhole is no longer a GOO, it is a Terror instead.
If this piece of info is unaccurate and is is still a GOO then Yog is destroyed and get his spellbook. Both happens.