We did not have any wine in the house so we made havdalah on Ice Coffee. Was that allowed? & is one permitted to make havdalah on whiskey?
You can definitely make havdala on whiskey, however the amount that you have to drink according to most poskim is maleh lugmov, a cheek-full, which is most of a revi’is, and you should pour the whiskey into a cup that contains a revi’is, as you would when making Havdalah on wine. Regarding ice coffee, it is controversial, because it isn’t considered a prominent drink, however if you are very stuck there are poskim to rely on.
M:B 296-9, Aruch Hashulchan 272-14, Igros Moshe O:CH 2-75, Shmiras Shabbos Khilchoso 60-4, Tzitz Eliezer 8-16.