The run flats on my BMW lasted the 5 1/2 years I owned the car, 37,500 miles, and still had 4mm tread left when I traded the car. To be fair 2 1/2 winters were spent on winter tyres, probably 8,000 miles but the run flats would have lasted the full 37,500 miles if needed.

I rotated front/rear twice a year and kept the pressures at BMW's figures, nothing special.