If my % of business mileage changed, not exclusive for non-business, I disposed the car, not sold it, how to calculate deprec. equivalent for stand. mileage deduction?

Just multiple the business miles by the depreciation equivalent for each year.  Then add up all of the years.

However, you said you disposed of the vehicle but did NOT sell it.  What happened to the vehicle?

Because the business percentage varied, if the disposition is taxable (which depends on exactly how the vehicle was disposed) you can NOT claim the disposition in the vehicle section.  The program does not do the proper calculations.   You need to either MANUALLY calculate things and report it in the "Sale of Business Property" section, or go to a tax professional.