That's only true up to a point. I suspect that if you exposed just about anything to 100,000 kelvin it ceased to look like any kind of matter we know anything about.
This experiment was performed thousands of times back in the 1950s and 1960s. A nuclear weapon's fireball is way hotter than 100,000K, and the exploding weapon contains lots of fissionable material and fission byproducts. The extreme temperatures don't destroy them, they just help spread it around.
Yes, but there is SOME temperature at which heating things up does start to cause things to act weirdly. You know, like in a fusion reactor. That definitely changes the radioactivity of certain elements.