I drove tractor trailers for a number of years. Here is what I recall about the grain elevators I visited. Grain is loaded from the top and unloaded from the bottom. (Gravity works and is free) I suppose an tornado or hurricane could tip one over but none of the ones I trucked into or out of would just "tip over" from improper loading/unloading.
No, unloading the bin will not tip it over. The grain will gravitate downward and will fill in what you have taken out till you reach the bottom. At that point the remaining uneven grain weighs to little to tip the bin