We're talking about a fractional decrease in resistance based on reduced alternator drag. Another way to look at it is the alternator is still taking care of regulating charging, it's not like the alternator is running at full output, full drag, all the time. It's just maintaining a higher voltage.
I'm pulling a trailer on varying terrain that usually weighs somewhere between 5k-6k depending on the trip. Hard to gauge any real MPG gain/loss. I'm usually around 10 towing.
And I'm running load E AT tires. Took about a 1.5mpg hit there.
MPG isn't really of concern to me on this pig. But honestly no noticeable change just from unplugging the battery sensor.