What happens if you side with Zelazny?
No, you'll never encounter Zelanzy or his mercs again in the game.
It also doesn't matter if you convince or lie to the doctor afterwards - you get the Praxis kit regardless.
The only difference in the various outcomes is how much experience you gain (you get the most for taking his team down, since you get XP for each takedown), and the fact that allowing Zelanzy to continue will cause the Belltower patrols in Hengsha to lessen slightly.