FAQ for
"Hercules: The Legendary Journeys" (1995) More at IMDbPro »

A good question. The first explanation is that the Olympian gods are capable of using their magic to time travel as has been proven in 'You are there' and 'Armegedon Now'. Therefore Strife travelled forwards in time with Ares into the 1990s and then returned to ancient Greece where he was killed by Callisto later in his personal timeline. This poses the problem of Ares potentially knowing the future which he shows no sign off but his ability to time travel may be limited solely to attempting to wreck Hercules' TV show or a higher power such as The Fates, Zeus or Hera prevent him from learning anything in the future that would upset destiny in the past. Second explanation is that Ares has somehow brought Strife back to life in the present day. Whilst characters who have died return from the dead all the time on 'Xena' and 'Hercules' for the most part gods don't, they stay dead (in fact Valesca aside unlike mortals of all religions it's unclear if deities even have an afterlife at all). It also seems unlikely that if Ares could bring another god back to life he would pick his nephew Strife whom he obviously despises, his niece Discord seems a far more likely candidate, not least as it's hinted they're also lovers. Third explanation is that by killing Strife Callisto actually changes history. When we see the 'Hercules' cast again in the later story 'For those of us just joining us' everything is the same EXCEPT that Strife no longer accompanies Ares, nor does he show up in Ares' two later appearances in the modern day on 'Xena'. Possibly the alteration in the timeline was engineered by Dahak as part of his world conquering scheme and was later corrected by the God of Eli or some other protaganist. Fourth theory is that the writers screwed up.