If the center differential in the RAV is an Open differential then removing the rear drive shaft would only hurt the vehicle. Open differentials send power to shaft of least resistance. So all of the power would try and go to the rear drive shaft, which isn't there.I know in my old 88 4x4 pickup with manual hubs that power and fuel economy drop when I click them in, even in 2H... When I’m actually using 4H or 4L the fuel mileage gets cut in half so removing the drive shaft in theory would help.. Hmmm might be worth a shot!
There is someone in "Fault's & Fixes" I believe who is having an issue involving the center dif where the car will only move when it's locked, which means something inside is possibly dead.