Its been my experience in dealing with many many run flat tires on tandem/tri axle equipment trailers the flat tire is still supporting much of its weight due to the equalizer bar.
I've unknowingly ran a flat tires at night till the tire wore away and the steel wheel made a huge spark show before I could tell the trailer had a flat tire. Now the operator has a ruined tire and wheel.
Quite a sight at 2 am on the morning on a lonesome two lane highway between two small towns in southeast CO at 60 mph.
I've also found cuts on the other tire in line with the shredded tire. BUT if the flat tire was caught in time and didn't shread at speed then no harm done to the next tire.