We had the Health Dept inspector discover inept valves, torn HVAC and missing roof vents in a home we lived in with many significant illnesses. How long does evidence of gasses
Remain in the home for additional testing. Toxicology experts confirm correlation with our medical reports-so we'd like tests done on the home if possible. Does Bacteria live
In the empty home and continue growing? The owners only eliminated mold, radon by tests
And chinese drywall was ruled out, but to our knowledge they left it abandoned & empty.

Impossible to answer. There may or may not be sewer gasses in an abandoned house. Bacteria aren't likely to settle onto surfaces from gasses but from backed up sewage. I would imagine that the code violations, the reports you've had so far, and the illnesses correlating should be enough to win a case.

Well your nice clean phrase sewer gas elements actually translates to Poop, correct? Well if a dog took a
Crap on the floor, depending on the overall moisture content of the local weather you might be steppin in or smelling **** for quite a while.

You have no idea what you're talking about-idiot!

The issue will be how well did they ventilate the house, what other forms of cleaning was done.
And what levels of material ( air borne) was there to start with, Remember mim levels may be within acceptable levels but it does not mean it along with other factors could not have been the cause.

I also doubt that you will get the home owner to allow the tests without a court order and of course you will have to pay for the tests up front ( and if they don't show anything have little recourse)