What is the worst case scenario between top of foundation and grade?

Your township has that information it varies by township
Depends where you live ( snow)
In general 4 to 6 inches.
Wost case scenario is grade flush to foundation or above it and sloped in toward wall.
I can answer better if you tell me why you asked the question Concrete slope min 1/4 per foot. Dirt min 3/4" per foot for good drainage