The World of Mutant X

The Mutant X series found Havok trapped in a parallel world where many of Earth's heroes suffered a fate far more tragic than their counterparts experienced in the mainstream Marvel Universe.

The group of heroes who formed the Defenders on that alternate Earth consisted of a cybernetic Stingray, a female Yellowjacket, a version of Doc Samson with green skin/hair, and a cryptic Dr. Strange with an affinity for the Nexus of All Realities (Mutant X '99 Annual). After the other Defenders perished while battling the powerful entity known as the Beyonder, Dr. Strange orchestrated a plan to send Havok back to the reality he called home (Mutant X #32).

This panel from Mutant X '99 Annual shows Havok's decision not to join the newly formed Defenders.