BTW, the campaign I'm currently DMing IS set in 1992 Detroit...
Tempest II: Not the brightest or most cautious hero, Tempest would probably try to persuade the Sentinels he's from the future. Fact is, the Tempest from 2003 is just the heir of the original hero by the same name (and same costume). By 1992, the original Tempest is still active and living, so Tempest II will be considered an imposter. Unable to prevent the disaster, he'll just fight Doc D and die if he has to.
Ombra: Acting quickly, he'd leave a message to his future self, including a detailed list of "future" (ie 1992-2003) disasters to avert: floods, earthquakes, eco-disasters, 9/11, you name it. Then he'd join the fray. He'd be most concerned with evacuation, as he's really out of his league with the likes of Destroyer. However, he might actually join the fight to buy time for evac. In this instance, however, he'd probably fight alongside Destroyer, not against him! Why? Well, Ombra knows Doc D activated his orbital cannon when he realised he was going to be defeated - so the best way to buy time is deleaying his defeat...