Interesting question that doesn't appear to have been asked before, but probably because it seems a bit obvious . . .
As RAB said, a lot would evaporate at the temperatures involved. The kitchen would likely be the recipient of the all pervasive aroma and could cause severe severe earache . . . from SWMBO, or even worse.
Being hygroscopic, the fondant will absorb water, but not necessarily a tincture of thymol. As the fondant cools, it might be possible to mix the thymol tincture into the fondant, but getting anything like a satisfactory distribution would take some doing and the odds of achieving success are remote.
Either way, it sounds like something that doesn't want to be done in a house.