Well, there's kind of a chain of intuitions here that are off by up to orders of magnitude. First, YBCO has a critical temperature of 93K, not 23K or so as you've suggested (albeit not as a value for YBCO). In other words, there have been advances in high temperature superconductors. Second, the magnets will not heat up from having large currents running through them. This is the point of superconductors. So, this estimate of resistivity is high by several orders of magnitude. Third, any estimate of the total energy of the hot plasma that gets us anywhere near verbiage hinting at explosions is too high by several orders of magnitude. You could typically extinguish a burning plasma by blowing gently on it. Finally, the thermal gradients aren't nearly so dire as, you know, 200e6K immediately next to 90K. There is typically over a meter of, in order: near-vacuum; inner wall; flowing lithium blanket; outer wall; and liquid nitrogen or other cryogenic coolant, all between the plasma and the magnets.

This is the farthest thing from a recipe for disaster.