You can reversal his ultimate back at him to deal a lot of damage and then easily headshot him.

When terminus uses his ult to get back alive, use reversal. If you time this ability right, you can fire over 3000 damage towards terminus and let your teammates or yourself finish him off.

Andro is one of the best counter champion to Terminus. You can absorb his ultimate using reversal and fire back for instant kill. Also whenever terminus uses his siphon use dashes to move behind him and shoot him from behind for easy kill.