Dredging up memories from high school chem: not actually impossible odds. Half-life means the time it takes for half of the atoms out of a given quantity to decay. There are 6.02E23 atoms per mole, and about 8 moles per kg for xenon. So with a large enough quality of xenon-124, some decay event should happen within a reasonable timeframe. Of course it’s still a tremendous technical feat to actually setup and detect such an event.