Use your Power Siphon to absorb his shots, and get behind a wall to recharge it. If you're running Decimation, you can shred half of his health down at max charge for your flanks/damages to finish him off, or at least force him to retreat and heal.
Atlas's Setback can shut down Terminus's ult entirely. Stay out of his range and fire it as soon as the animation is finished, and he'll be stuck with 1HP once Setback ends. You can also use Second Chance to avoid the explosion if you can't get away.
Not much you can do against Inara. If you're set on killing her, buy Bulldozer 3 and help your teammates tear down her deployables. Shadow Step her ult if she tries to hit you with it. Don't go in alone, because you don't have the power to finish it.
Lian's biggest advantage is superior range/pokes. Use the map to your advantage and try to sneak up on her, and once you're close enough you should be able to take her out. Use Shadow Step to evade her Presence and especially her ult.
Koga is fast and hard to target, plus he is able to remove marks by dashing. Fight him at midrange to keep him from getting behind you. I recommend getting at least harmonious 3, his ult will end up healing your full health.