Has anyone found a Doctor/Medic in Zion that can cure addictions?

Daniel.

What do you do after he's gone OH NO!?!?

Awesome! Thank you, Longknife!!

It svcks that after you beat the DLC ALL of the people disappear and all whats left is the animals.

Only the named characters disappeared in my playthrough, but that probably depends on what ending you pursued.

If you evacuated Zion, the Sorrows and Dead Horses leave and White Legs roam Zion, which is good, since White Legs have good weapons ( AMR, 12.7 mm SMG etc). If you destroy the White Legs, both of the other 2 tribes remain, but are praticaly useless. No matter what ending you choose, all named characters will leave. But about doctors, theres only Daniel, and if youv beat it, you'll have to scrounge Fixer from one of the caves or buildings around Zion. Also, if youv already beaten HH, just leave and go to a doctor, you can always go and leave Zion whenever you want after beating it.

I wish they added generic service NPCs after the DLC or better yet they should have been there the whole time.

A "Sorrows Medicine Man" and a "Dead Horse Trader" would have been quite helpful to have. There should have been a few other non-aligned people just rummaging around the park, sort of adventurer/scavenger types like you.

Maybe some of them could trade.