On entering the bathroom, I discovered the powder, and the odor, were INCHES of talcum powder on the floor where this person apparently "bathed" with the talcum powder, then carried/spread it throughout the apartment.

Silly smokers - just because they can't smell the odor of smoke on themselves does not mean you won't notice the odor of smoke. ;)

-Have the HVAC unit cleaned out and use -Rent an Ozone or hire a company to clean the air-Replace the drywall all together-Another option is to clean, paint with KILZ (removing most of the odor but not all), and to simply market that unit as a smoking unit.Hopefully this helps Nathan

Then you also have the odor and the damage the fire did.Just be prepared and knowledgeable before you jump into the deal.

As soon as I and renewed the lease the tenant wrote me this long message with all these thing wrong, including drain smells bad(she’s been putting bleach down the drain to kill the odor, the lights in the kitchen and bedroom are flickering(this ones easily fixable) & the bathroom floor is in-caving because of water damage(she suggested a new shower door).

When this happened in one of my buildings, I went into the complaining neighbor's unit and smelled the odor myself. 

Last tenant cooked some amazing Indian food but with the spices etc the new tenant is concerned the odor may still be prevalent when they move in. 

@Adam Martin: I haven't had a cat in 20 years (but I had many growing up), so I think I can detect the odor and I didn't.