Simple resolution:
Use stone shape, passwall, rock to mud, adamantine spoons, an earth elemental, or large burrowing animal to circumvent it.
If you want to complicate it, here's a multiple choice solution:
A. If any of the PCs has ever run into a SoA (or equivalent), or someone makes the appropriate knowledge rolls, Leave It Alone. The risk factor involved in messing with what might be a portal, gate, or other weird effect versus it being a SoA is too high. IOW: "Hmmm... this might be a gateway to riches and wealth, or we can get obliterated beyond the ability of Resurrection to bring us back. What do you think, guys? Yeah, me too. Let's try a different dungeon."
B. If you absolutely must pass beyond this point (to Save The World, for example), and all the tests in A failed, cast Augury: "If we pass through this inky blot of utter nothingness, will it benefit our mission?" If the answer is "Weal", chuck a summoned monster through it and see if it survived. If the answer is "Woe", react as if any of the tests in A identified it as a SoA.
C. Ignore both of the above. Use stone shape, passwall, rock to mud, adamantine spoons, an earth elemental, large burrowing animal, or any other method to circumvent it. Even a Wish is cheaper than annihilation.
D. Safest choice: None of the above. Hire another party of adventurers to mess with it instead.
I usually go with C. It's fun making the DM redraw his Dungeon of Doooooom maps.
... see the spoiler at post #5
