> What if the wrapped index is used to construct an invalid pointer?

Constructing an invalid pointer in rust is UB, yes, but integer wraparound is not.

> What if the integer is used to read the wrong data to a disk, or corrupt data on disk by writing to the wrong location?

Then it is a very bad bug.

> What if the program controls a nuclear power plant and the integer causes the control system to fail, causing memory errors due to radiation from the meltdown?

Then it is a very very bad bug.

> What if the wrapped integer causes the program to output the true name of god, and the programmer, in their last minutes of existence, looks up to see, overhead, without any fuss, the stars going out?

Ok, you got me, this one is UB.