This may gross some of the more squeamish of you out, so don't read it if you are easily offended. Many years ago, we had a driver who had a heart attack and died in one of our trucks while parked at a service plaza on the Indiana toll road. It was late summer and he was in an enclosed cab for a few days before he was found. Not pretty. Anyway, the county coroners office told us of a service they recommended to clean up all kinds of crime scenes as well as those similar to ours where they found dead bodies in homes that had been there long enough for them to literally liquify into the floors, etc. Long story short, we hired these people and when they got through with the truck you couldn't tell anything had ever happened. Some things needed replaced, like the mattress for instance, but most were just sanitized with whatever kind of chemicals and cleaners they use for that sort of thing.
I've seen (smelled) cigarrette smoke interiors that I'd be surprised if anything would work on but if anything would do it, I think it'd be the stuff these kinds of companies use. If I were you, I'd call your local coroners office and find out who they recommend for those kinds of clean-ups in your area. Good luck.