Ganache is the same thing you find in "truffles" and they don't refrigerate those! Mind you the chocolate to cream ratio is higher in truffles than icing. But the same principal applies as with buttercream icings: the fat-to-sugar ratio is such that bacterial growth is inhibited for a while. Compared to mousse, well, usually there is a LOT more cream in mousse (so, not enough sugar to stabilize), and also often enough, uncooked eggs (although I'd use pasteurized personally). So refrigeration is a must. That's the layman's answer, anyway
Icing ganache (1:1 ratio) is supposed to be good at room temp for about 2 days, but can be refrigerated or even frozen.
It is hard to find a good guide for what can sit out and what cannot because nobody can take that legal liability risk, since there is no guarantee that you prepare an item within the exact specifications needed to render it safe to sit out. That's why it's such a popular question, and you will see it asked time and again. Heck I think I have even asked it from time to time!
Anyway with regard to fondant sweating/bleeding that also can be turned into a nonissue if you use Sa tin Ice or the Michele Foster's recipe. MMF definitely sweats and can certainly bleed if the colors are dark enough (ask me how I know this). Still, if you use MMF and your colors are light enough, you can refrigerate if you wait a good long time for the moisture to evaporate at room temp.
If it were me, I would refrigerate today just for the heck of it (that's one less day it's been sitting out) but I would not refrigerate after applying fondant.