One of the Avengers' greatest fears is what would happen if Sentry's full powers were unleashed on the Marvel Universe, and in a What If...? story, the nightmare became a reality. In What If...? #200 from Marvel Comics, the publisher asked what would have happened if Norman Osborn's Siege of Asgard was successful? The answer is particularly brutal, as it would have led to Sentry destroying the entire world after unleashing the Void.
Sentry is one of the most chaotic forces in the entire Marvel Universe, with the hero's powers of one million exploding suns seemingly having no upper limit. While Sentry has tried to be a hero and work alongside the Avengers, his unpredictable nature has made him one of the most destructive beings ever, as his dark side, the Void, turns the hero and his extraordinary abilities into a world-eating monster. To stop the Void, Sentry has had his memory of his powers wiped from the world's existence multiple times. But, the hero always seems to return, including in the Siege storyline. Sentry worked alongside the Dark Avengers in that comic and destroyed Asgard - as his powers went out of control.
While Norman Osborn, Sentry, and the Dark Avengers were unsuccessful in their Siege of Asgard, What If...? #200 by Marc Guggenheim, Dave Wilkins, Lucio Parrillo, and Dave Lanphear from Marvel Comics imagined what would happen if they had won against Earth's Mightiest Heroes. The issue asks, what if Sentry killed Ares days earlier and was rested going into battle against the Avengers? It turns out that it would lead to the destruction of Earth. Sentry puts his fist through Luke Cage, chops Captain America's head off with his shield, and kills Bullseye and Emma Frost after learning about his wife Lindy's death. As he loses control, Sentry gets pushed over the edge and the Void is unleashed, brutally murdering the Dark Avengers.
The Void would kill all the Avengers, other heroes, villains, and the population of Earth. Uatu the Watch is left observing the planet's destruction as Sentry's dark side uses his powers to engulf the world. The cosmic being admits that it's only a matter of time before Sentry consumes the Moon and the rest of the Marvel Universe.
While the What If...? story takes place outside of continuity, it proved that Sentry's full unleashed powers would not just kill Earth's Mightiest Heroes but could take down the Marvel Universe as a whole. He brutalizes some of the most powerful heroes before turning on the planet and consuming it. It's an amazing display of power that shows why Sentry and others have worked so hard to suppress the Void. With his dark side released, even the Avengers are helpless against Sentry.