https://www.1000bulbs.com/product/116183/VENTURE-86501.html

I find these lamps quite interesting. It says that when one arc tube burns out it switches to the other. How does this work? Also, if the one arctube explodes, wouldn't that take out the second arctube with it?

This I've seen first with HPS.

Because of the discharge characteristics (you have to first exceed the ignition voltage, then the ionization builds, forcing the voltage down), always the one with the lower ignition voltage strikes, leaving the other effectively OFF.
The idea behind the twin arctubes in HPS is: One of them has lower voltage, e.g. due to the manufacturing tolerances, so ignites first. When it lights normally, nothing else happens and the other remains OFF, just waiting. Once the first extingushes because of the (with HPS common) EOL cycling, the time before it cools down to be able to reignited the other, colder one becomes the one with the lower voltage and so gets ignited by the ignitor and so takes over the service.
The catch is, this works only, if the only problem is the impossibility to ignite one of the arctube, so in fact just a cycling lamp fault. But any fault more, when one of the tubes loose integrity and so leaks out mean the first discharge to ignite will be somewhere in the outer.And if the failure of the first is so violent it damages the other tube, this concept fails as well.

It seems to me Venture jut took this concept and implemented with MH. The question is, if it really works.
Although this works quite well as a means of redundancy with HPS (they do just cycle as the main EOL), I have strong doubts it will work with MH as well. Of course, if one tube starts just cycling, this will work. But with MH the other failure modes are more frequent and because there this concept does not help, I doubt it is that effective with MH to justify the extra cost.

Both arc tubes age about the same as each time power is cycled off then on the opposite arc tube strikes up

This shouldn`t get a chance to explode either, the ONLY reason halide lamps explode, is because their end users leaves them in running way beyond their rated life, if this did explode, it would be the last remaining `good` tube, and by then, it wouldn`t matter if it then damaged the `used` tube.

The only problem I see with this is, Venture halide tubes almost always `change shape` during running, because both tubes are so close together, in horizontal operation, this could lead to one tube interfering with the other, (or in a worse case scenario), sticking to each other!

"Venture" and "long life" ? -_-