Cruise, we have 3 tickets, but only 2 of us are going. We lose money either way(canceling the 3rd) I know. but what would happen otherwise?

Were you all going to be in one room? You need to contact the cruise company- the pricer per person is often different for three people in a room versus two. They might be willing to apply what was paid for the third ticket to the price for two. I take it you didn't buy travel insurance. So it's unlikely you're going to get any money back, but it might depend on how soon the cruise is.

yes