It would probably kill him from strain, but David West has the raw potential to wipe out planets if he tried, and Lor'I'Anar is not far behind... Though the gods might interfere and stop them. (Between Earth and Pyrroth).
Though he has not put in an appearance, Tennigrath, Lord of the Void, boss of Morgalis The Wizard and First of the Outsider Gods almost tanked Jack Diamond's (Strange Awakening, Diamond in the Rough, Blood Diamond) universe at the dawn of time and is still around, barely kept at bay by the sacrifice of the First Archmage.
As the "universe" is virtual, well, the guy who created it, the father of The First Player, could tank it (and kill his cash cow, and possible vehicle for world domination) in Digital Cowboy Dane.
So far, that's pretty much it.