Room temperature super conductors don't quench. Or at least, not until they reach the temperature at which they no longer work as superconductors, which for this one is 127 degrees Celsius.
That does make for an interesting failure mode if anything should every cause a small spot on a longer conductor to reach that temperature...
No, at the breach it will just burn up until the arc dissipates. But it will be an impressive fireworks display. A superconductor is in the end just another conductor, it has a well defined current carrying capacity while superconducting and if it stops doing that then that current will suddenly see an increased resistance, how much current is moving through it at the time it failes determines how fast and how violent it burns out when it goes, but it won't be unlike another transmission line failure. Those are still very impressive:
Quite a bit more than chemical, in other words, the chief problem being what happens if it quenches. Or the cables break.
And cost.