fafhrd said:We can pray that a very liberal treatment of Mindblank and distance will keep the PCs in the game.
Indeed that's a pretty liberal reading of Mindblank but as to distance it seems that Kostotchie's area of effect is limited by sight. Whether that is somewhat limited like a dragon or the tarrasque's frightful presence would need clarification. Personally a range of 300 ft is likely adequate.
Of course assuming that mindblank has that liberal of a reading makes one wonder why there isn't a hefty directed epic spell that cancels mindblank across a huge area (say a demiplane )