This question comes up every few months and the basic answer is NO it is not safe to travel more than a few hundred feet when one tire in a pair of duals fails.
However, I also know that some locations on the side of the road are not safe and if you decide that moving is the best option what can you do?
In the tire industry, there are tables that provide information on how
slow you need to drive as you increase the tire load above its normal
load capacity if you want to try and prevent a second tire failure.
Basically, you need to run no faster than 40 mph if you are running 107% of the rated load.
If you want to run 113% you can drive no faster than 30 and the max speed drops to 20 mph if the overload is +18%.
The above also limit the "max travel time at those speeds to 2 hours with a minimum 1/2 hour "cool Down" time each 2 hours.
Since our RV owner was running at 200% load I would estimate that maximum speed he could travel without doing damage to the "good" tire to be no faster than 5 mph and even that is questionable as there are also distance limits for those conditions.
If you have a tire failure, no matter the reason, you need to change out the failed tire and should not attempt to "limp" home on its companion. If you are concerned for your safety on the side of the road, you need to be aware that driving over 5 mph means you MUST have the companion tire also replaced. No matter its age. As always when changing tires in a dual position you must also match the pair for OC.
Many in a thread said "slow down" but I doubt that any were thinking of less than 20 mph. Some may have driven considerable distance at some "reduced speed" but is each case the companion tire should have also been replaced.